ToDo: diffs FF142-FF143

[earthlng]

FF143 release date: Sep. 16th 2025

FF143 release notes
FF143 for developers
FF143 security advisories

---

110 diffs ( 56 new, 36 gone, 18 different )

new in v143.0:

pref("browser.search.visualSearch.featureGate", false);
pref("browser.urlbar.importantDates.featureGate", false);
pref("browser.urlbar.market.featureGate", false);

changed in v143.0:

pref("browser.download.enableDeletePrivate", true); // prev: false

---

ignore

click me for details

==NEW

pref("browser.contentanalysis.print_set_foreground_window", true);
pref("browser.ipProtection.guardian.endpoint", "https://vpn.mozilla.org/");
pref("browser.ipProtection.log", false);
pref("browser.ipProtection.variant", "");
pref("browser.lna.warning.infoURL", "https://support.mozilla.org/%LOCALE%/kb/control-personal-device-local-network-permissions-firefox");
pref("browser.ml.pageAssist.enabled", false);
pref("browser.newtabpage.activity-stream.discoverystream.personalization.override", false);
pref("browser.newtabpage.activity-stream.discoverystream.promoCard.enabled", false);
pref("browser.newtabpage.activity-stream.discoverystream.promoCard.visible", true);
pref("browser.newtabpage.activity-stream.discoverystream.shortcuts.force_log.enabled", false);
pref("browser.newtabpage.activity-stream.widgets.focusTimer.interaction", false);
pref("browser.newtabpage.activity-stream.widgets.focusTimer.showSystemNotifications", false);
pref("browser.newtabpage.activity-stream.widgets.lists.interaction", false);
pref("browser.newtabpage.activity-stream.widgets.lists.maxListItems", 100);
pref("browser.newtabpage.activity-stream.widgets.lists.maxLists", 10);
pref("browser.newtabpage.activity-stream.widgets.system.enabled", false);
pref("browser.newtabpage.sponsor-protection.enabled", true);
pref("browser.tabs.groups.hoverPreview.enabled", false);
pref("browser.unexpectedScriptLoad.logLevel", "Warn");
pref("browser.urlbar.market.minKeywordLength", 0);
pref("browser.urlbar.suggest.importantDates", true);
pref("browser.urlbar.suggest.realtimeOptIn", true);
pref("content.cors.use_triggering_principal", false);
pref("devtools.webconsole.groupSimilarMessages", true);
pref("dom.custom_elements.relaxed_names.enabled", true);
pref("dom.movebefore.enabled", false);
pref("dom.serviceworkers.loadingCachedScriptOnWorkerThread.enabled", false);
pref("dom.webgpu.blocked-domains", "easyeda.com,*.easyeda.com");
pref("dom.webgpu.external-texture.enabled", false);
pref("gfx.canvas.accelerated.max-export-surface-memory", 536870912);
pref("gfx.canvas.accelerated.max-export-surfaces", 100);
pref("gfx.skia.dithering", false);
pref("javascript.options.ducktyped_errors", false);
pref("javascript.options.objectfuse_for_global", true);
pref("javascript.options.wasm_exception_force_stack_trace", false);
pref("layout.css.moz-appearance.enabled", true);
pref("layout.css.moz-appearance.webidl.enabled", false);
pref("layout.css.scroll-state.enabled", false);
pref("layout.css.text-autospace.enabled", false);
pref("layout.css.text-decoration-trim.enabled", false);
pref("messaging-system.profile.singleProfileMessaging.disable", true);
pref("network.http.http3.enable_certificate_compression_brotli", true);
pref("network.http.http3.enable_certificate_compression_zlib", true);
pref("network.http.http3.enable_certificate_compression_zstd", true);
pref("pdfjs.enableComment", false);
pref("permissions.default.local-network", 0);
pref("permissions.default.localhost", 0);
pref("security.block_parent_unrestricted_js_loads.temporary", false);
pref("security.hide_parent_unrestricted_js_loads_warning.temporary", false);
pref("security.parent_unrestricted_js_loads.skip_jshacks", false);
pref("services.sync.prefs.sync.browser.ipProtection.enabled", true);
pref("sidebar.verticalTabs.dragToPinPromo.dismissed", false);
pref("urlclassifier.enabled_mode", 3);

==REMOVED, RENAMED or HIDDEN

pref("apz.scrollbarbuttonrepeat.enabled", true);
pref("browser.download.deletePrivateChosen", false);
pref("browser.newtabpage.activity-stream.discoverystream.editorsPicksHeader.enabled", false);
pref("browser.newtabpage.activity-stream.discoverystream.essentialReadsHeader.enabled", false);
pref("browser.newtabpage.activity-stream.discoverystream.isCollectionDismissible", true);
pref("browser.newtabpage.activity-stream.discoverystream.recentSaves.enabled", false);
pref("browser.newtabpage.activity-stream.discoverystream.saveToPocketCard.enabled", true);
pref("browser.newtabpage.activity-stream.discoverystream.saveToPocketCardRegions", "");
pref("browser.newtabpage.activity-stream.discoverystream.shortcuts.personalization.locale-config", "en-US,en-GB,en-CA");
pref("browser.newtabpage.activity-stream.discoverystream.shortcuts.personalization.region-config", "");
pref("browser.newtabpage.activity-stream.discoverystream.sponsored-collections.enabled", false);
pref("browser.newtabpage.activity-stream.newtabShortcuts.refresh", true);
pref("browser.newtabpage.activity-stream.showRecentSaves", true);
pref("browser.search.param.search_rich_suggestions", "fen");
pref("browser.search.rustSelector.featureGate", true);
pref("browser.urlbar.fakespot.minKeywordLength", 4);
pref("browser.urlbar.fakespot.suggestedIndex", -1);
pref("browser.urlbar.suggest.fakespot", true);
pref("devtools.every-frame-target.enabled", true);
pref("devtools.webconsole.groupWarningMessages", true);
pref("dom.disable_tab_focus_to_root_element", true);
pref("extensions.formautofill.creditCards.heuristics.fathom.highConfidenceThreshold", "0.95");
pref("extensions.pocket.refresh.hideRecentSaves.enabled", false);
pref("extensions.userScripts.mv3.enabled", true);
pref("extensions.webextensions.userScripts.enabled", true);
pref("javascript.options.experimental.import_attributes", true);
pref("layout.css.element-content-none.enabled", false);
pref("layout.css.moz-user-input.enabled", false);
pref("layout.css.size-adjust.enabled", true);
pref("security.csp.reporting.limit.timespan", 2);
pref("security.mixed_content.upgrade_display_content.audio", true);
pref("security.mixed_content.upgrade_display_content.image", true);
pref("security.mixed_content.upgrade_display_content.video", true);
pref("security.pki.netscape_step_up_policy", 1);
pref("sidebar.revamp.defaultLauncherVisible", true);
pref("svg.embedder-prefers-color-scheme.content.enabled", true);

==CHANGED

pref("browser.contextual-services.contextId.rotation-in-days", 30); // prev: 0
pref("browser.ml.linkPreview.shift", false); // prev: true
pref("browser.newtabpage.activity-stream.support.url", "https://support.mozilla.org/1/firefox/143.0/WINNT/en-US/new-tab"); // prev: "https://support.mozilla.org/1/firefox/142.0/WINNT/en-US/new-tab"
pref("browser.screenshots.folderList", 4); // prev: 1
pref("browser.tabs.groups.smart.enabled", true); // prev: false
pref("browser.taskbarTabs.enabled", true); // prev: false
pref("dom.private-attribution.submission.enabled", false); // prev: true
pref("dom.quotaManager.loadQuotaFromSecondaryCache", true); // prev: false
pref("dom.quotaManager.originInitialization.updateOriginMetadata", true); // prev: false
pref("extensions.formautofill.addresses.supportedCountries", "US,CA,GB,FR,DE,BR,ES,JP"); // prev: "US,CA,GB,FR,DE"
pref("font.name-list.sans-serif.x-beng", "Nirmala Text, Vrinda, Akaash, Likhan, Ekushey Punarbhaba"); // prev: "Vrinda, Akaash, Likhan, Ekushey Punarbhaba"
pref("layout.css.details-content.enabled", true); // prev: false
pref("layout.css.grid-multi-pass-track-sizing.enabled", true); // prev: false
pref("layout.css.overflow-moz-hidden-unscrollable.enabled", false); // prev: true
pref("layout.details.force-block-layout", false); // prev: true
pref("network.dnsCacheExpirationGracePeriod", 600); // prev: 60
pref("pdfjs.highlightEditorColors", "yellow=#FFFF98,green=#53FFBC,blue=#80EBFF,pink=#FFCBE6,red=#FF4F5F,yellow_HCM=#FFFFCC,green_HCM=#53FFBC,blue_HCM=#80EBFF,pink_HCM=#F6B8FF,red_HCM=#C50043"); // prev: "yellow=#FFFF98,green=#53FFBC,blue=#80EBFF,pink=#FFCBE6,red=#FF4F5F"

[earthlng]

some bugzilla tickets

• apz.scrollbarbuttonrepeat.enabled
  Bug 1980041 - Remove a bunch of code dealing with scrollbars that don't have a mediator.

• browser.contentanalysis.print_set_foreground_window
  Bug 1980225 - fix race condition with content analysis and printing to file

• browser.contextual-services.contextId.rotation-in-days
  Bug 1981851 - Default to rotating the context ID every 15 days.
  Bug 1981851 - Default to rotating the context ID every 30 days.
  Revert "Bug 1981851 - Default to rotating the context ID every 30 days.

• browser.download.deletePrivateChosen
  Bug 1981153 - Fix up static pref list for delete private downloads feature -

• browser.download.enableDeletePrivate
  Bug 1981504 - Turn on do not delete downloads feature for private browsing -
  Revert "Bug 1790641 - Only delete downloaded files in private browsing if deletePrivate pref is set to true -

• browser.ipProtection.guardian.endpoint
  Bug 1976022 - Add a guardian client
  Revert "Bug 1976022 - Add a guardian client

• browser.ipProtection.log
  Bug 1984733 - Add logging for IPProtection.

• browser.ipProtection.variant
  Bug 1982138 - Add a variant Nimbus variable and pref for ipProtection.

• browser.lna.warning.infoURL
  Bug 1978017 - Add learn more URL to localhost and local network access permission prompts.

• browser.ml.linkPreview.shift
  Bug 1972800 - default shift keyboard shortcut to false for Link Preview -
  Revert "Bug 1972800 - default shift keyboard shortcut to false for Link Preview -

• browser.ml.pageAssist.enabled
  Bug 1978472 - Page Buddy Feature Foundation
  Revert "Bug 1978472 - Page Buddy Feature Foundation

• browser.newtabpage.activity-stream.discoverystream.editorsPicksHeader.enabled
  Bug 1972352 - Remove Recommend Stories title experiment overrides

• browser.newtabpage.activity-stream.discoverystream.essentialReadsHeader.enabled
  Bug 1972352 - Remove Recommend Stories title experiment overrides

• browser.newtabpage.activity-stream.discoverystream.isCollectionDismissible
  Bug 1982772 - Remove Pocket sponsored collections

• browser.newtabpage.activity-stream.discoverystream.personalization.override
  Bug 1978177 - Newtab fixup tests failing because of pref changed

• browser.newtabpage.activity-stream.discoverystream.promoCard.visible
  Bug 1980018 – Add promo card styles for sections layout.

• browser.newtabpage.activity-stream.discoverystream.recentSaves.enabled
  Bug 1953330 - Remove code related to recent saves (from Pocket)

• browser.newtabpage.activity-stream.discoverystream.saveToPocketCard.enabled
  Bug 1946817 - Remove all code left around the save to pocket card button

• browser.newtabpage.activity-stream.discoverystream.saveToPocketCardRegions
  Bug 1946817 - Remove all code left around the save to pocket card button

• browser.newtabpage.activity-stream.discoverystream.shortcuts.personalization.locale-config
  Bug 1986921 - [GENAI-1826] - Turn on shortcut interaction logging
  Bug 1972900 - Newtab smart shortcuts feed integration

• browser.newtabpage.activity-stream.discoverystream.shortcuts.personalization.region-config
  Bug 1986921 - [GENAI-1826] - Turn on shortcut interaction logging
  Bug 1972900 - Newtab smart shortcuts feed integration

• browser.newtabpage.activity-stream.discoverystream.sponsored-collections.enabled
  Bug 1982772 - Remove Pocket sponsored collections

• browser.newtabpage.activity-stream.newtabShortcuts.refresh
  Bug 1972369 – graduate shortcuts refresh experiment.

• browser.newtabpage.sponsor-protection.enabled
  Bug 1978161 - Add infrastructure for proxying and monitoring the bandwidth usage of browsers from sponsor clicks.
  Revert "Bug 1978161 - Add infrastructure for proxying and monitoring the bandwidth usage of browsers from sponsor clicks.

• browser.screenshots.folderList
  Bug 1974983 Screenshot location should fallback to browser.download.folderList by default.
  Revert "Bug 1974983 Screenshot location should fallback to browser.download.folderList by default.
  Bug 1838053 - Add pref which allows users to choose to save Screenshots to the OS screenshots directory.

• browser.search.param.search_rich_suggestions
  Bug 1980449 - Remove redundant search_rich_suggestions preference from firefox.js.

• browser.search.rustSelector.featureGate
  Bug 1976694 - Remove the JavaScript based Search Engine Selector code.
  Bug 1967490 - Enable the Rust based search engine selector for late beta & release.
  Bug 1956384 - Set rustSelector.featureGate flag to true on Nightly and early Beta.
  Bug 1952713 - Update rust search engine selector integration to handle the search configuration overrides collection.

• browser.search.visualSearch.featureGate
  Bug 1977965 - Add a "Search Image" content context menu item for performing visual searches.

• browser.tabs.groups.hoverPreview.enabled
  Bug 1976283: Create a pref for showing or hiding the tab group hover preview panel

• browser.tabs.groups.smart.enabled
  Bug 1978921 - pref on smart tab grouping by default while restricting to en-*

• browser.taskbarTabs.enabled
  Bug 1980306 - Turn on Web Apps (working title Taskbar Tabs) by default.
  Revert "Bug 1980306 - Turn on Web Apps (working title Taskbar Tabs) by default

• browser.unexpectedScriptLoad.logLevel
  Bug 1979341: Add the style and content to the dialog

• browser.urlbar.fakespot.minKeywordLength
  Bug 1968096 - Remove desktop Fakespot Suggest code.

• browser.urlbar.fakespot.suggestedIndex
  Bug 1968096 - Remove desktop Fakespot Suggest code.

• browser.urlbar.importantDates.featureGate
  Bug 1983376 - Allow features that use dynamic Rust suggestions to be their own SuggestProvider.

• browser.urlbar.market.featureGate
  Bug 1983377 - Make one class per realtime suggestion type that serves both opt-in and online suggestions.

• browser.urlbar.market.minKeywordLength
  Bug 1979478: Add result context menu for Market suggestions

• browser.urlbar.suggest.fakespot
  Bug 1968096 - Remove desktop Fakespot Suggest code.

• browser.urlbar.suggest.importantDates
  Bug 1983376 - Allow features that use dynamic Rust suggestions to be their own SuggestProvider.

• browser.urlbar.suggest.realtimeOptIn
  Bug 1983377 - Make one class per realtime suggestion type that serves both opt-in and online suggestions.

• content.cors.use_triggering_principal
  Bug 1985652: Use triggeringPrincipal rather than loadingPrincipal for CORS checks, if triggeringPrincipal is from an extension.
  Bug 1970490: Use loading principal (rather than triggering principal) for CORS checks, by default.
  Revert "Bug 1970490: Use loading principal (rather than triggering principal) for CORS checks, by default.

• devtools.every-frame-target.enabled
  Bug 1978535 - [devtools] Remove unused preference devtools.every-frame-target.enabled

• devtools.webconsole.groupSimilarMessages
  Bug 1615206 - [devtools] Make the "Group similar message" setting control repeating messages.

• devtools.webconsole.groupWarningMessages
  Bug 1615206 - [devtools] Make the "Group similar message" setting control repeating messages.

• dom.custom_elements.relaxed_names.enabled
  Bug 1974274 - Relax custom element name restrictions
  Revert "Bug 1974274 - Relax custom element name restrictions

• dom.disable_tab_focus_to_root_element
  Bug 1982307 - Remove dom.disable_tab_focus_to_root_element.

• dom.movebefore.enabled
  Bug 1983688 - Enable moveBefore in release,
  Bug 1923880, ParentNode.moveBefore(),
  Revert "Bug 1923880, ParentNode.moveBefore(),

• dom.private-attribution.submission.enabled
  Bug 1979093 - Remove website advertising settings.

• dom.quotaManager.loadQuotaFromSecondaryCache
  Bug 1982790 - QM: Enable L2 quota info cache unconditionally;
  Bug 1978609 - QM: Enable origin metadata updates and use of L2 quota info cache on all Nightly platforms;
  Bug 1976451 - QM: Enable origin metadata updates and use of L2 quota info cache on all desktop Nightly platforms;
  Bug 1973433 - QM: Enable use of L2 quota info cache during repository initialization on Nightly and Linux;
  Bug 1973429 - QM: Add pref to control use of L2 quota info cache during repository initialization;

• dom.quotaManager.originInitialization.updateOriginMetadata
  Bug 1982790 - QM: Enable L2 quota info cache unconditionally;
  Bug 1978609 - QM: Enable origin metadata updates and use of L2 quota info cache on all Nightly platforms;
  Bug 1976451 - QM: Enable origin metadata updates and use of L2 quota info cache on all desktop Nightly platforms;
  Bug 1973422 - QM: Enable origin metadata file updates after initialization on Nightly and Linux;
  Bug 1972548 - QM: Add pref to control origin metadata file updates after initialization;

• dom.serviceworkers.loadingCachedScriptOnWorkerThread.enabled
  Bug 1967540: Creating a pref to force load cached service workers on main thread, default to true for now.r=edenchuang

• dom.webgpu.blocked-domains
  Bug 1980392: Block WebGPU for easyeda.com, configurable by pref.
  Revert "Bug 1980392: Block WebGPU for easyeda.com, configurable by pref.

• dom.webgpu.external-texture.enabled
  Bug 1986246 - Let WebGPU external textures ride the trains on Macos.
  Bug 1983594 - Enable webgpu external textures on windows.
  Bug 1982866 - Make WebGPU external texture support configurable via a pref and blocklistable.
  Revert "Bug 1982866 - Make WebGPU external texture support configurable via a pref and blocklistable.

• extensions.formautofill.addresses.supportedCountries
  Bug 1978053 - Enable Address Autofill for Brazil, Spain and Japan
  Bug 1970065 - Enable Address Autofill for UK
  Bug 1901246, enable address autofill capture in fr/de regions,

• extensions.formautofill.creditCards.heuristics.fathom.highConfidenceThreshold
  Bug 1977780 - Remove "Only Visible Input" and "High Confidence" Constraint for Credit Card Field Detection

• extensions.pocket.refresh.hideRecentSaves.enabled
  Bug 1953330 - Remove code related to recent saves (from Pocket)

• extensions.userScripts.mv3.enabled
  Bug 1943057 - Remove extensions.userScripts.mv3.enabled pref
  Bug 1943050 - Enable userScripts API by default on desktop

• extensions.webextensions.userScripts.enabled
  Bug 1943057 - Remove pref extensions.webextensions.userScripts.enabled

• font.name-list.sans-serif.x-beng
  Bug 1977076 - Prefer Nirmala Text as default sans-serif for Bangla on Windows.

• gfx.canvas.accelerated.max-export-surface-memory
  Bug 1980552 - Limit the memory usage of in-flight export surfaces.

• gfx.canvas.accelerated.max-export-surfaces
  Bug 1980552 - Limit the memory usage of in-flight export surfaces.

• gfx.skia.dithering
  Bug 1976791 - Add a capability to enable dithering to linear gradient in DrawTargetSkia

• javascript.options.ducktyped_errors
  Bug 1977364 - Disable support for ducktyped errors.

• javascript.options.experimental.import_attributes
  Bug 1982227 - Part 6: Remove import attributes pref

• javascript.options.objectfuse_for_global
  Bug 1983823 part 1 - Extend constant-property optimization to the global lexical environment.
  Bug 1981133 part 7 - Add ObjectFuse and use it for the global object.

• javascript.options.wasm_exception_force_stack_trace
  Bug 1978633 - wasm: Add a pref to force stack trace collection in wasm exceptions.

• layout.css.details-content.enabled
  Bug 1941406: Enable support for the ::details-content pseudo-element.
  Revert "Bug 1941406: Enable support for the ::details-content pseudo-element.

• layout.css.element-content-none.enabled
  Bug 1979755 - Remove experimental, never-shipped support for content: none on elements.

• layout.css.grid-multi-pass-track-sizing.enabled
  Bug 1957244 - Enable layout.css.grid-multi-pass-track-sizing.enabled by default.

• layout.css.moz-appearance.enabled
  Bug 1977489 - Hide MozAppearance from CSSStyleProperties
  Revert "Bug 1977489 - Hide MozAppearance from CSSStyleProperties

• layout.css.moz-appearance.webidl.enabled
  Bug 1977489 - Hide MozAppearance from CSSStyleProperties
  Revert "Bug 1977489 - Hide MozAppearance from CSSStyleProperties

• layout.css.moz-user-input.enabled
  Bug 1935314 - Remove -moz-user-input CSS property

• layout.css.overflow-moz-hidden-unscrollable.enabled
  Bug 1978450: Turn off layout.css.overflow-moz-hidden-unscrollable.enabled on all branches.

• layout.css.scroll-state.enabled
  Bug 1978108 - Add basic parsing for scroll-state container type.

• layout.css.size-adjust.enabled
  Bug 1872780 - Remove layout.css.size-adjust.enabled pref
  Revert "Bug 1872780 - Remove layout.css.size-adjust.enabled pref

• layout.css.text-autospace.enabled
  Bug 1980104 - Add style system support for the text-autospace property.

• layout.css.text-decoration-trim.enabled
  Bug 1979913 - Add text-decoration-trim to the style system.

• layout.details.force-block-layout
  Bug 1941406: Remove the Nightly-only guard from about:config pref "layout.details.force-block-layout".
  Revert "Bug 1941406: Enable support for the ::details-content pseudo-element.

• messaging-system.profile.singleProfileMessaging.disable
  Bug 1979402 - Set singleProfileMessaging mitigation to off by default

• network.dnsCacheExpirationGracePeriod
  Bug 1937022 - increased dns cache grace period to 10min.
  Bug 1936996 - Convert dns prefs to StaticPrefs

• network.http.http3.enable_certificate_compression_brotli
  Bug 1927797 - Enable brotli in neqo_glue
  Revert "Bug 1927797 - Enable brotli in neqo_glue

• network.http.http3.enable_certificate_compression_zlib
  Bug 1927797 - Enable zlib in neqo_glue

• network.http.http3.enable_certificate_compression_zstd
  Bug 1927797 - Enable zstd in neqo_glue using c zstd implementation
  Revert "Bug 1927797 - Enable brotli in neqo_glue

• permissions.default.localhost
  Bug 1960618 - localhost permissions UI implementation.

• permissions.default.local-network
  Bug 1972350 - Local Network Permission UI impl.

• security.block_parent_unrestricted_js_loads.temporary
  Bug 1979341: Wire up the script reporting and pref setting

• security.csp.reporting.limit.timespan
  Bug 1978054 - Remove security.csp.reporting.limit.timespan pref.

• security.hide_parent_unrestricted_js_loads_warning.temporary
  Bug 1979341: Create a pref to disable the notification bar, and ensure Nimbus can control it

• security.mixed_content.upgrade_display_content.audio
  Bug 1978062 - Remove individual security.mixed_content.upgrade_display_content prefs.

• security.mixed_content.upgrade_display_content.image
  Bug 1978062 - Remove individual security.mixed_content.upgrade_display_content prefs.

• security.mixed_content.upgrade_display_content.video
  Bug 1978062 - Remove individual security.mixed_content.upgrade_display_content prefs.

• security.parent_unrestricted_js_loads.skip_jshacks
  Bug 1979341: Add a test

• security.pki.netscape_step_up_policy
  Bug 1980431 - remove NetscapeStepUpMatchesServerAuth from TrustDomains.

• services.sync.prefs.sync.browser.ipProtection.enabled
  Bug 1979218 - Add enrollment checks for IP Protection.
  Revert "Bug 1979218 - Add enrollment checks for IP Protection.

• sidebar.revamp.defaultLauncherVisible
  Bug 1978425 - Default defaultLauncherVisible to false and fix the nimbus variable/pref confusion
  Revert "Bug 1978425 - Default defaultLauncherVisible to false and fix the nimbus variable/pref confusion

• sidebar.verticalTabs.dragToPinPromo.dismissed
  Bug 1966541 - Add promo card in the vertical tab strip to notify users they can pin tabs
  Revert "Bug 1966541 - Add promo card in the vertical tab strip to notify users they can pin tabs

• svg.embedder-prefers-color-scheme.content.enabled
  Bug 1849937 - Remove svg.embedder-prefers-color-scheme.content.enabled pref

• urlclassifier.enabled_mode
  Bug 1981870 - Added pref to disable classfier