This is difference between the default preference of Firefox 129.0 beta 6 and one of 128.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 128.0Firefox 129.0 beta 6
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.backup.scheduled.idle-threshold-seconds undefined 300
browser.backup.scheduled.minimum-time-between-backups-seconds undefined 3600
browser.backup.sqlite.pages_per_step 5 50
browser.backup.sqlite.step_delay_ms 250 50
browser.display.use_document_fonts.icon_font_allowlist Material Icons, Material Icons Extended, Material Icons Outlined, Material Icons Round, Material Icons Sharp, Material Icons Two Tone, Google Material Icons, Google Material Icons Filled, Material Symbols Outlined, Material Symbols Round, Material Symbols Rounded, Material Symbols Sharp Material Icons, Material Icons Extended, Material Icons Outlined, Material Icons Round, Material Icons Sharp, Material Icons Two Tone, Google Material Icons, Google Material Icons Filled, Material Symbols Outlined, Material Symbols Round, Material Symbols Rounded, Material Symbols Sharp, Google Symbols, FontAwesome
browser.ml.chat.hideLocalhost undefined true
browser.ml.chat.prompt.prefix I’m on page "%currentTabTitle%" with "%selection|12000%" selected. I’m on page "%tabTitle%" with "%selection|12000%" selected.
browser.ml.chat.prompts.0 {"label":"Summarize","value":"Please summarize the selection using precise and concise language. Highlight the main themes and conclusions. Use headers and bulleted lists in the summary, to make it scannable. Maintain the meaning of the selection."} {"label":"Summarize","value":"Please summarize the selection using precise and concise language. Use headers and bulleted lists in the summary, to make it scannable. Maintain the meaning and factual accuracy.","id":"summarize"}
browser.ml.chat.prompts.1 {"label":"Simplify language","value":"Please rewrite the selection in plain, clear language suitable for a general audience without specialized knowledge. Use all of the following tactics: simple vocabulary; short sentences; active voice; examples where applicable to make explanations clearer; explanations for jargon and technical terms; headers and bulleted lists for scannability. Maintain factual accuracy while simplifying."} {"label":"Simplify Language","value":"Please rewrite the selection in plain, clear language suitable for a general audience without specialized knowledge. Use all of the following tactics: simple vocabulary; short sentences; active voice; headers and bulleted lists for scannability. Maintain meaning and factual accuracy.","id":"simplify"}
browser.ml.chat.prompts.2 {"label":"Quiz me","value":"Please create questions related to the selection. Ask the questions one by one. Wait for my response before moving on to the next question. Evaluate each response. Ask a variety of types of questions, like multiple choice, true or false and short answer."} {"label":"Quiz Me","value":"Please quiz me on this selection. Ask me a variety of types of questions, for example multiple choice, true or false, and short answer. Wait for my response before moving on to the next question.","id":"quiz","targeting":"!provider|regExpMatch('gemini')"}
browser.ml.chat.sidebar undefined true
browser.newtabpage.activity-stream.discoverystream.endpoints https://getpocket.cdn.mozilla.net/,https://firefox-api-proxy.cdn.mozilla.net/,https://spocs.getpocket.com/ https://getpocket.cdn.mozilla.net/,https://firefox-api-proxy.cdn.mozilla.net/,https://spocs.getpocket.com/,https://merino.services.mozilla.com/
browser.newtabpage.activity-stream.discoverystream.locale-weather-config undefined en-US,en-GB,en-CA
browser.newtabpage.activity-stream.discoverystream.merino-provider.enabled undefined false
browser.newtabpage.activity-stream.discoverystream.merino-provider.endpoint undefined merino.services.mozilla.com
browser.newtabpage.activity-stream.discoverystream.thumbsUpDown.enabled undefined false
browser.newtabpage.activity-stream.discoverystream.thumbsUpDown.searchTopsitesCompact undefined false
browser.newtabpage.activity-stream.discoverystream.topicSelection.enabled undefined false
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.newtabpage.activity-stream.weather.locationSearchEnabled false true
browser.sessionstore.log.appender.file.logOnSuccess false true
browser.sessionstore.loglevel Warn Debug
browser.urlbar.quicksuggest.sponsoredIndex -1 0
browser.urlbar.showSearchTerms.featureGate false true
browser.urlbar.trending.enabledLocales en-US, en-CA undefined
browser.urlbar.yelp.featureGate false true
browser.urlbar.yelp.minKeywordLength 0 4
browser.urlbar.yelp.suggestedIndex 0 undefined
cookiebanners.ui.desktop.enabled false true
devtools.client-side-throttling.enable undefined false
devtools.debugger.javascript-tracing-max-depth undefined 200
devtools.high-contrast-mode-support undefined false
devtools.inspector.rule-view.starting-style undefined true
dom.document.edit_command.contentReadOnly.enabled true false
dom.document.edit_command.insertBrOnReturn.enabled true false
dom.event.keypress.key.allow_lone_surrogate true false
dom.events.mouse-pointer-boundary.keep-enter-targets-after-over-target-removed false true
dom.events.textevent.enabled false true
dom.forms.always_allow_key_and_focus_events.enabled false true
dom.forms.fieldset_disable_only_descendants.enabled false true
dom.ipc.disableContentProcessReuse undefined false
dom.security.https_first_schemeless false true
dom.shadowdom.new_caretPositionFromPoint_behavior.enabled undefined false
dom.svg.pathSeg.enabled false undefined
dom.vibrator.enabled true false
dom.w3c_pointer_events.dispatch_click_as_pointer_event undefined true
extensions.InstallTrigger.enabled true false
extensions.formautofill.addresses.capture.requiredFields street-address,postal-code,address-level1,address-level2 undefined
extensions.formautofill.addresses.supportedCountries US,CA US,CA,FR,DE
extensions.webcompat-reporter.enabled false true
fission.enforceBlocklistedPrefsInSubprocesses false true
gfx.canvas.remote.recycle-used-data-surface false true
gfx.canvas.remote.use-canvas-translator-event undefined true
gfx.remote-texture.wait-owner-at-image-host true false
gfx.webrender.debug.slow-cpu-frame-threshold undefined 10.0
gfx.webrender.debug.surface-promotion-logging undefined false
gfx.webrender.svg-filter-effects undefined false
gfx.webrender.svg-filter-effects.also-convert-css-filters undefined false
gfx.webrender.svg-filter-effects.also-use-for-docshell-fecolormatrix undefined false
gfx.webrender.svg-filter-effects.feblend undefined true
gfx.webrender.svg-filter-effects.fecolormatrix undefined true
gfx.webrender.svg-filter-effects.fecomponenttransfer undefined true
gfx.webrender.svg-filter-effects.fecomposite undefined true
gfx.webrender.svg-filter-effects.feconvolvematrix undefined false
gfx.webrender.svg-filter-effects.fediffuselighting undefined false
gfx.webrender.svg-filter-effects.fedisplacementmap undefined false
gfx.webrender.svg-filter-effects.fedropshadow undefined true
gfx.webrender.svg-filter-effects.feflood undefined true
gfx.webrender.svg-filter-effects.fegaussianblur undefined true
gfx.webrender.svg-filter-effects.feimage undefined false
gfx.webrender.svg-filter-effects.femerge undefined true
gfx.webrender.svg-filter-effects.femorphology undefined false
gfx.webrender.svg-filter-effects.feoffset undefined false
gfx.webrender.svg-filter-effects.fespecularlighting undefined false
gfx.webrender.svg-filter-effects.fetile undefined false
gfx.webrender.svg-filter-effects.feturbulence undefined false
gfx.webrender.svg-filter-effects.opacity undefined true
gfx.webrender.svg-filter-effects.toalpha undefined true
identity.fxaccounts.telemetry.clientAssociationPing.enabled undefined false
javascript.options.experimental.float16array undefined true
javascript.options.experimental.regexp_duplicate_named_groups undefined true
javascript.options.mem.gc_incremental_slice_ms 10 5
javascript.options.use_emulates_undefined_fuse true undefined
javascript.options.use_fdlibm_for_sin_cos_tan false true
javascript.options.wasm_exnref false true
javascript.options.wasm_experimental_compile_pipeline undefined false
layout.css.field-sizing.enabled undefined false
layout.css.intrinsic-size-first-letter.enabled undefined true
layout.css.letter-spacing.model 0 2
layout.css.starting-style-at-rules.enabled false true
layout.css.transition-behavior.enabled false true
layout.dynamic-reflow-roots.enabled false true
layout.overflow-underflow.content.enabled true false
media.media-capabilities.enabled true undefined
media.webrtc.tls_tunnel_for_all_proxy undefined true
memory.phc.enabled false true
network.auth.confirmAuth.enabled true false
network.cookie.chips.partitionLimitByteCapacity undefined 10240
network.cookie.chips.partitionLimitDryRun undefined true
network.cookie.chips.partitionLimitEnabled undefined true
network.cookie.thirdparty.nonsecureSessionOnly false undefined
network.cookie.thirdparty.sessionOnly false undefined
network.dns.mock_HTTPS_RR_domain undefined
network.dns.native_https_query false true
network.early-hints.over-http-v1-1.enabled undefined true
network.fetchpriority.adjustments.media.auto undefined 0
network.fetchpriority.adjustments.media.high undefined 0
network.fetchpriority.adjustments.media.low undefined 10
network.http.http3.retry_different_ip_family false true
network.jar.record_failure_reason false true
network.jar.require_size_match true undefined
network.predictor.enable-prefetch false true
network.send_OnDataFinished.cssLoader false true
pdfjs.enableHWA undefined false
pdfjs.enableHighlightFloatingButton false true
plugins.rewrite_youtube_embeds true false
privacy.annotate_channels.strict_list.enabled false true
reader.colors_menu.enabled false true
reader.improved_text_menu.enabled false true
remote.active-protocols 3 1
security.disallow_non_local_systemprincipal_in_tests undefined false
security.remote_settings.crlite_filters.enabled false true
security.sandbox.warn_unprivileged_namespaces undefined true
security.ssl3.ecdhe_ecdsa_aes_128_sha true false
security.ssl3.ecdhe_ecdsa_aes_256_sha true false
security.tls.client_hello.send_p256_keyshare undefined true
security.tls.enable_certificate_compression_brotli false true
security.tls.enable_certificate_compression_zlib false true
security.tls.enable_certificate_compression_zstd undefined true
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.passwords.validation.enabled undefined true
services.sync.prefs.sync.network.cookie.thirdparty.sessionOnly true undefined
sidebar.main.tools undefined aichat,syncedtabs,history
sidebar.verticalTabs undefined false
sidebar.visibility undefined always-show
signon.signupDetection.enabled true undefined
startup.homepage_override_nimbus_disable_wnp undefined false
svg.nearestAndFarthestViewportElement.enabled true false
test.ime_content_observer.assert_valid_cache undefined false
toolkit.telemetry.enabled false true
toolkit.telemetry.geckoview.batchDurationMS 5000 undefined
toolkit.telemetry.geckoview.maxBatchStalenessMS 60000 undefined
toolkit.telemetry.user_characteristics_ping.opt-out undefined false
toolkit.telemetry.user_characteristics_ping.send-once undefined false
ui.new-webcompat-reporter.send-more-info-link false true
webgl.1.request_es2 undefined true
widget.non-native-theme.win11.scrollbar.round-track undefined false