This is difference between the default preference of Firefox 121.0 beta 9 and one of 121.0.1. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 120.0Firefox 121.0 beta 3
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.firefox-view.virtual-list.enabled undefined false
browser.newtabpage.activity-stream.asrouter.providers.snippets {"id":"snippets","enabled":false,"type":"remote","url":"https://snippets.cdn.mozilla.net/%STARTPAGE_VERSION%/%NAME%/%VERSION%/%APPBUILDID%/%BUILD_TARGET%/%LOCALE%/%CHANNEL%/%OS_VERSION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION%/","updateCycleInMs":14400000} undefined
browser.newtabpage.activity-stream.asrouter.providers.whats-new-panel {"id":"whats-new-panel","enabled":true,"type":"remote-settings","collection":"whats-new-panel","updateCycleInMs":3600000} {"id":"whats-new-panel","enabled":false,"type":"remote-settings","collection":"whats-new-panel","updateCycleInMs":3600000}
browser.newtabpage.activity-stream.feeds.snippets false undefined
browser.search.param.search_rich_suggestions undefined fen
browser.translations.newSettingsUI.enable undefined false
browser.translations.select.enable undefined false
browser.urlbar.richSuggestions.featureGate undefined true
cookiebanners.bannerClicking.executeOnce true undefined
cookiebanners.bannerClicking.maxTriesPerSiteAndSession undefined 3
devtools.inspector.compatibility.enabled true undefined
devtools.inspector.showRulesViewEnterKeyNotice undefined true
dom.about_newtab_sanitization.enabled false undefined
dom.cache.privateBrowsing.enabled false true
dom.enable_largest_contentful_paint false true
dom.media.webcodecs.force-osx-h264-enabled undefined false
dom.screenwakelock.enabled undefined false
dom.screenwakelock.testing undefined false
dom.security.setdocumenturi undefined false
dom.select.showPicker.enabled false true
dom.webcomponents.shadowdom.declarative.enabled undefined false
dom.webnotifications.privateBrowsing.enableDespiteLimitations undefined false
dom.workers.importScripts.enforceStrictMimeType false true
extensions.formautofill.heuristics.captureOnFormRemoval undefined false
extensions.webcompat-reporter.enabled false true
gfx.canvas.remote.default-buffer-size undefined 32768
gfx.canvas.remote.drop-buffer-limit undefined 100
gfx.canvas.remote.drop-buffer-milliseconds undefined 10000
gfx.canvas.remote.event-timeout-ms undefined 2
gfx.canvas.remote.max-spin-count undefined 500
gfx.canvas.remote.max_default_buffers undefined 256
intl.hyphenate-capitalized.fi undefined true
intl.icu4x.segmenter.enabled false true
javascript.options.arraybuffer_transfer undefined true
javascript.options.mem.gc_parallel_marking_threshold_mb 200 16
layout.css.allow-mixed-page-sizes false true
layout.css.basic-shape-rect.enabled false true
layout.css.basic-shape-xywh.enabled false true
layout.css.initial-document-transparency undefined 3
layout.css.margin-rules.enabled undefined false
layout.css.motion-path-basic-shapes.enabled false true
layout.css.motion-path-coord-box.enabled false true
layout.css.motion-path-offset-position.enabled false true
layout.css.motion-path-ray.enabled false true
layout.css.motion-path-url.enabled false true
layout.css.page-orientation.enabled false true
layout.scroll.disable-pixel-alignment undefined false
media.aboutwebrtc.auto_refresh true undefined
media.aboutwebrtc.auto_refresh.connection_log_section undefined false
media.aboutwebrtc.auto_refresh.media_ctx_section undefined false
media.aboutwebrtc.auto_refresh.peerconnection_section undefined true
media.aboutwebrtc.auto_refresh.user_modified_config_section undefined true
media.ffmpeg.encoder.enabled undefined false
media.navigator.video.red_ulpfec_enabled false true
memory.phc.min_ram_mb undefined 8000
network.cookie.cookieBehavior.optInPartitioning undefined false
network.dns.max_any_priority_threads 3 24
network.dns.max_high_priority_threads 5 40
network.http.http2.websockets false true
network.http.http3.max_accumlated_time_ms undefined 1
network.send_OnDataFinished false true
network.send_OnDataFinished.html5parser false true
network.send_OnDataFinished.nsInputStreamPump false true
network.ssl_tokens_cache_use_only_once true undefined
network.trr.hard_fail_on_extended_error undefined true
network.url.useDefaultURI false true
pdfjs.enableHighlightEditor undefined false
pdfjs.highlightEditorColors undefined yellow=#FFFF98,green=#53FFBC,blue=#80EBFF,pink=#FFCBE6,red=#FF4F5F
permissions.default.screen-wake-lock undefined 1
privacy.webrtc.legacyGlobalIndicator false undefined
security.csp.external-hashes.enabled true undefined
security.csp.script-src-attr-elem.enabled true undefined
security.csp.style-src-attr-elem.enabled true undefined
security.csp.unsafe-hashes.enabled true undefined
security.csp.wasm-unsafe-eval.enabled true undefined
security.webauthn.enable_conditional_mediation undefined true
security.webauthn.enable_macos_passkeys false true
security.webauthn.show_ms_settings_link undefined false
services.sync.prefs.sync.browser.newtabpage.activity-stream.feeds.snippets true undefined
services.sync.prefs.sync.browser.search.widget.inNavBar true undefined
signon.management.page.fileImport.enabled false true
svg.use-element.data-url-href.allowed undefined false
toolkit.telemetry.enabled false true
urlclassifier.trackingAnnotationSkipURLs google.com/recaptcha/,*.google.com/recaptcha/ google.com/recaptcha/,*.google.com/recaptcha/,d3vox9szr7t2nm.cloudfront.net
webgl.gl_khr_no_error true false
widget.gtk.libadwaita-colors.enabled undefined true