This is difference between the default preference of Firefox 121.0 beta 3 and one of 120.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 120.0Firefox 121.0 beta 3
app.normandy.test-prefs.bool undefined false
app.normandy.test-prefs.integer undefined 0
app.normandy.test-prefs.string undefined
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.contentanalysis.enabled undefined false
browser.contentanalysis.is_per_user undefined true
browser.contentanalysis.pipe_path_name undefined path_user
browser.contentanalysis.silent_notifications undefined false
browser.contentblocking.report.vpn_regions as,at,be,ca,ch,de,es,fi,fr,gb,gg,ie,im,io,it,je,mp,my,nl,nz,pr,se,sg,uk,um,us,vg,vi ca,my,nz,sg,gb,gg,im,io,je,uk,vg,as,mp,pr,um,us,vi,de,fr,at,be,ch,es,it,ie,nl,se,fi,bg,cy,cz,dk,ee,hr,hu,lt,lu,lv,mt,pl,pt,ro,si,sk
browser.firefox-view.search.enabled undefined false
browser.mailto.dualPrompt undefined false
browser.mailto.dualPrompt.os undefined false
browser.mailto.prompt.os undefined true
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.safebrowsing.passwords.enabled false undefined
browser.safebrowsing.provider.google4.lists goog-badbinurl-proto,goog-downloadwhite-proto,goog-phish-proto,googpub-phish-proto,goog-malware-proto,goog-unwanted-proto,goog-harmful-proto,goog-passwordwhite-proto goog-badbinurl-proto,goog-downloadwhite-proto,goog-phish-proto,googpub-phish-proto,goog-malware-proto,goog-unwanted-proto,goog-harmful-proto
browser.tabs.documentchannel.parent-controlled false true
browser.tabs.documentchannel.speculative-load undefined false
browser.topsites.contile.sov.enabled false true
browser.translations.autoTranslate false undefined
browser.translations.languageIdentification.useFastText false undefined
browser.urlbar.quickactions.enabled undefined true
browser.urlbar.quickactions.showPrefs undefined true
browser.urlbar.quicksuggest.contextualOptIn undefined false
browser.urlbar.quicksuggest.contextualOptIn.sayHello undefined false
browser.urlbar.quicksuggest.contextualOptIn.topPosition undefined true
browser.urlbar.shortcuts.quickactions undefined true
browser.urlbar.showSearchTerms.featureGate false true
browser.urlbar.suggest.quickactions undefined true
browser.urlbar.trending.featureGate undefined true
cookiebanners.bannerClicking.executeOnce undefined true
cookiebanners.service.enableGlobalRules false true
cookiebanners.ui.desktop.enabled false true
devtools.debugger.pause-on-debugger-statement undefined true
devtools.performance.recording.power.external-url undefined
devtools.toolbox.force-chrome-prefs true undefined
dom.animations.mainthread-synchronization-with-geometric-animations true false
dom.document.edit_command.contentReadOnly.enabled true false
dom.document.edit_command.insertBrOnReturn.enabled true false
dom.element.customstateset.enabled undefined false
dom.element.invokers.enabled undefined false
dom.event.keypress.key.allow_lone_surrogate true false
dom.forms.always_allow_pointer_events.enabled false true
dom.forms.fieldset_disable_only_descendants.enabled false true
dom.iframe_lazy_loading.enabled false true
dom.resize_observer.last_reported_size_invalid true undefined
dom.select.showPicker.enabled undefined false
dom.webgpu.hal-labels undefined false
dom.workers.importScripts.enforceStrictMimeType false true
editor.block_inline_check.use_computed_style false true
editor.join_split_direction.compatible_with_the_other_browsers true undefined
extensions.InstallTrigger.enabled true false
extensions.abuseReport.amoFormEnabled undefined false
extensions.abuseReport.amoFormURL undefined https://addons.mozilla.org/%LOCALE%/%APP%/feedback/addon/%addonID%/
extensions.webcompat-reporter.enabled false true
fission.enforceBlocklistedPrefsInSubprocesses false true
javascript.options.use_fdlibm_for_sin_cos_tan false true
javascript.options.wasm_tail_calls false true
layout.css.allow-mixed-page-sizes false true
layout.css.bucket-attribute-names.enabled true undefined
layout.css.has-selector.enabled false true
layout.css.modern-range-pseudos.enabled undefined false
layout.css.scroll-anchoring.absolute-update undefined true
layout.css.text-align.justify-only-after-last-tab undefined true
layout.css.text-indent-keywords.enabled undefined true
layout.css.text-wrap-balance.enabled false true
layout.css.webkit-range-pseudos.enabled false undefined
layout.dynamic-reflow-roots.enabled false true
media.allow-audio-non-utility true false
media.autoplay.block-webaudio true undefined
media.videocontrols.lock-video-orientation false undefined
media.webrtc.platformencoder false true
memory.phc.enabled false true
network.auth.use_redirect_for_retries false true
network.cookie.sameSite.noneRequiresSecure false true
network.early-hints.enabled false true
network.http.http2.move_to_pending_list_after_network_change false true
network.http.http3.retry_different_ip_family false true
network.jar.record_failure_reason false true
network.predictor.enable-prefetch false true
network.send_OnDataFinished undefined false
network.send_OnDataFinished.html5parser undefined false
network.send_OnDataFinished.nsInputStreamPump undefined false
network.send_OnDataFinished_after_progress_updates undefined false
pdfjs.viewerCssTheme 0 undefined
plugins.rewrite_youtube_embeds true false
privacy.annotate_channels.strict_list.enabled false true
privacy.exposeContentTitleInWindow undefined true
privacy.exposeContentTitleInWindow.pbm undefined true
security.disallow_non_local_systemprincipal_in_tests undefined false
security.remote_settings.crlite_filters.enabled false true
security.ssl3.ecdhe_ecdsa_aes_128_sha true false
security.ssl3.ecdhe_ecdsa_aes_256_sha true false
security.webauthn.enable_macos_passkeys undefined false
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.passwords.validation.enabled undefined true
svg.nearestAndFarthestViewportElement.enabled true false
toolkit.telemetry.dap_helper https://helper1.dap.cloudflareresearch.com/v02 https://dap.services.mozilla.com
toolkit.telemetry.dap_helper_owner Cloudflare Mozilla
toolkit.telemetry.dap_leader https://dap-02.api.divviup.org https://dap-07-1.api.divviup.org/
toolkit.telemetry.dap_task1_taskid undefined
toolkit.telemetry.dap_visit_counting_enabled undefined false
toolkit.telemetry.dap_visit_counting_experiment_list undefined []
toolkit.telemetry.enabled false true
ui.mouse.right_click.collapse_selection.stop_if_non_collapsed_selection undefined true
ui.mouse.right_click.collapse_selection.stop_if_non_editable_node undefined false
ui.new-webcompat-reporter.enabled undefined false
ui.new-webcompat-reporter.reason-dropdown undefined 0
ui.new-webcompat-reporter.send-more-info-link undefined true
urlclassifier.disallow_completions goog-downloadwhite-digest256,base-track-digest256,mozstd-trackwhite-digest256,content-track-digest256,mozplugin-block-digest256,mozplugin2-block-digest256,goog-passwordwhite-proto,ads-track-digest256,social-track-digest256,analytics-track-digest256,base-fingerprinting-track-digest256,content-fingerprinting-track-digest256,base-cryptomining-track-digest256,content-cryptomining-track-digest256,fanboyannoyance-ads-digest256,fanboysocial-ads-digest256,easylist-ads-digest256,easyprivacy-ads-digest256,adguard-ads-digest256,social-tracking-protection-digest256,social-tracking-protection-facebook-digest256,social-tracking-protection-linkedin-digest256,social-tracking-protection-twitter-digest256,base-email-track-digest256,content-email-track-digest256 goog-downloadwhite-digest256,base-track-digest256,mozstd-trackwhite-digest256,content-track-digest256,mozplugin-block-digest256,mozplugin2-block-digest256,ads-track-digest256,social-track-digest256,analytics-track-digest256,base-fingerprinting-track-digest256,content-fingerprinting-track-digest256,base-cryptomining-track-digest256,content-cryptomining-track-digest256,fanboyannoyance-ads-digest256,fanboysocial-ads-digest256,easylist-ads-digest256,easyprivacy-ads-digest256,adguard-ads-digest256,social-tracking-protection-digest256,social-tracking-protection-facebook-digest256,social-tracking-protection-linkedin-digest256,social-tracking-protection-twitter-digest256,base-email-track-digest256,content-email-track-digest256
urlclassifier.passwordAllowTable goog-passwordwhite-proto undefined