This article shows the difference between the default preferences of Firefox 142.0 beta 9 and Firefox 141.0.3. The diff table below is generated using my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 141.0.3Firefox 142.0 beta 9
app.releaseNotesURL https://www.mozilla.org/%LOCALE%/firefox/%VERSION%/releasenotes/?utm_source=firefox-browser&utm_medium=firefox-desktop&utm_campaign=whatsnew https://www.mozilla.org/%LOCALE%/firefox/%VERSION%beta/releasenotes/?utm_source=firefox-browser&utm_medium=firefox-desktop&utm_campaign=whatsnew
app.releaseNotesURL.aboutDialog https://www.mozilla.org/%LOCALE%/firefox/%VERSION%/releasenotes/?utm_source=firefox-browser&utm_medium=firefox-desktop&utm_campaign=about-dialog https://www.mozilla.org/%LOCALE%/firefox/%VERSION%beta/releasenotes/?utm_source=firefox-browser&utm_medium=firefox-desktop&utm_campaign=about-dialog
app.update.channel release beta
app.update.url.details https://www.mozilla.org/%LOCALE%/firefox/notes https://www.mozilla.org/%LOCALE%/firefox/beta/notes
app.update.url.manual https://www.mozilla.org/%LOCALE%/firefox/new?reason=manual-update https://www.mozilla.org/%LOCALE%/firefox/beta?reason=manual-update
browser.crashReports.dontShowBefore undefined 0
browser.link.alternative_click.block_javascript undefined true
browser.ml.chat.maxLength undefined 7000
browser.newtabpage.activity-stream.discoverystream.placements.contextualBanners undefined
browser.newtabpage.activity-stream.discoverystream.placements.contextualBanners.counts undefined
browser.newtabpage.activity-stream.discoverystream.placements.spocs newtab_spocs newtab_stories_1, newtab_stories_2, newtab_stories_3, newtab_stories_4, newtab_stories_5, newtab_stories_6
browser.newtabpage.activity-stream.discoverystream.placements.spocs.counts 6 1,1,1,1,1,1
browser.newtabpage.activity-stream.discoverystream.spoc-positions 1,5,7,11,18,20 2,4,8,13,17,20
browser.newtabpage.activity-stream.feeds.listsfeed undefined true
browser.newtabpage.activity-stream.feeds.timerfeed undefined true
browser.newtabpage.activity-stream.support.url https://support.mozilla.org/1/firefox/141.0.3/Linux/en-US/new-tab https://support.mozilla.org/1/firefox/142.0/Linux/en-US/new-tab
browser.newtabpage.activity-stream.system.showSponsoredCheckboxes false true
browser.newtabpage.activity-stream.widgets.focusTimer.enabled undefined true
browser.newtabpage.activity-stream.widgets.lists.enabled undefined true
browser.newtabpage.activity-stream.widgets.system.focusTimer.enabled undefined false
browser.newtabpage.activity-stream.widgets.system.lists.enabled undefined false
browser.newtabpage.resource-mapping.log undefined false
browser.newtabpage.trainhopAddon.xpiBaseURL undefined https://archive.mozilla.org/pub/system-addons/newtab/
browser.tabs.groups.smart.searchTopicEnabled undefined true
browser.urlbar.deduplication.enabled false true
browser.urlbar.merino.ohttpConfigURL undefined
browser.urlbar.merino.ohttpRelayURL undefined
devtools.netmonitor.response.ui.limit 10240 undefined
dom.animations.commit-styles-endpoint-inclusive false true
dom.document.name_getter_prevent_shadowing.enabled undefined false
dom.element.commandfor.on_details.enabled undefined false
dom.enable_web_task_scheduling false true
dom.object_embed.codebase.enabled undefined false
dom.quotaManager.loadQuotaFromSecondaryCache undefined false
dom.quotaManager.originInitialization.updateOriginMetadata undefined false
dom.security.credentialmanagement.identity.heavyweight.enabled false undefined
dom.security.credentialmanagement.identity.lightweight.enabled false undefined
dom.security.enforceIPCBasedPrincipalVetting true undefined
dom.security.setdocumenturi true undefined
dom.shadowdom.selection_across_boundary.enabled false true
dom.svg.pathSegment.enabled true undefined
dom.urlpattern.enabled undefined true
dom.viewTransitions.wr-old-capture true undefined
dom.webnotifications.icon_encoding_utf8.enabled undefined true
dom.workers.timeoutmanager true undefined
extensions.formautofill.creditCards.os-auth.locked.enabled undefined false
extensions.webcompat-reporter.enabled false true
extensions.webextensions.restrictedDomains accounts-static.cdn.mozilla.net,accounts.firefox.com,addons.cdn.mozilla.net,addons.mozilla.org,api.accounts.firefox.com,content.cdn.mozilla.net,discovery.addons.mozilla.org,install.mozilla.org,oauth.accounts.firefox.com,profile.accounts.firefox.com,support.mozilla.org,sync.services.mozilla.com accounts-static.cdn.mozilla.net,accounts.firefox.com,addons.cdn.mozilla.net,addons.mozilla.org,api.accounts.firefox.com,content.cdn.mozilla.net,discovery.addons.mozilla.org,oauth.accounts.firefox.com,profile.accounts.firefox.com,support.mozilla.org,sync.services.mozilla.com
gfx.webrender.dithering undefined false
gfx.webrender.layer-compositor undefined false
javascript.options.wasm_unroll_loops false true
layout.css.align-content.blocks.enabled true undefined
layout.css.animation-composition.enabled true undefined
layout.css.contain-intrinsic-size.enabled true undefined
layout.css.h1-in-section-ua-styles.enabled false undefined
layout.css.has-selector.enabled true undefined
layout.css.has-slotted-selector.enabled true undefined
layout.css.heading-selector.enabled undefined false
layout.css.hyphenate-limit-chars.enabled true undefined
layout.css.import-supports.enabled true undefined
layout.css.overscroll-behavior.enabled true undefined
layout.css.text-indent-keywords.enabled true undefined
layout.css.text-wrap-balance.enabled true undefined
layout.css.transform-box-content-stroke.enabled true undefined
layout.css.typed-om.enabled undefined false
layout.display_partial_background_images true undefined
layout.testing.scrollbars.always-hidden undefined false
mathml.unknown_mrow.enabled undefined true
media.getusermedia.camera.fake.force undefined false
media.hardware-video-encoding.enabled undefined true
media.hardware-video-encoding.force-enabled undefined false
media.navigator.video.default_resize_mode undefined 0
media.navigator.video.resize_mode.enabled undefined false
media.webspeech.recognition.force_enable false undefined
network.cookie.chips.partitionLimitDryRun true false
network.cookie.skip_browsing_context_check_in_parent_for_testing undefined false
network.http.http3.max_gso_segments undefined 10
network.lna.address_space.local.override undefined
network.lna.address_space.private.override undefined
network.lna.address_space.public.override undefined
nimbus.profilesdatastoreservice.sync.enabled undefined false
places.frecency.pages.alternative.maxDaysFromToday 60 undefined
privacy.trackingprotection.allow_list.hasMigratedCategoryPrefs undefined false
security.disallow_privileged_data_subdocuments_loads true undefined
security.disallow_privileged_https_script_loads true undefined
security.disallow_privileged_https_stylesheet_loads true undefined
security.disallow_privileged_https_subdocuments_loads true undefined
security.disallow_privileged_no_finaluri_loads true undefined
security.integrity_policy.stylesheet.enabled undefined false
security.pki.crlite_mode 3 2
sidebar.installed.extensions undefined
signon.management.page.os-auth.locked.enabled undefined false
svg.image-element.force-sync-load undefined true
svg.nearestAndFarthestViewportElement.enabled false undefined
svg.use-element.data-url-href.allowed false undefined
termsofuse.acceptedDate undefined 0
termsofuse.acceptedVersion undefined 0
termsofuse.bypassNotification undefined false
termsofuse.currentVersion undefined 4
termsofuse.minimumVersion undefined 4
toolkit.telemetry.enabled false true
widget.gtk.non-native-titlebar-buttons.enabled true undefined