This is difference between the default preference of Firefox 135.0 beta 7 and one of 134.0.2. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 134.0.2Firefox 135.0 beta 7
accessibility.typeaheadfind.wrappedSoundURL 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.multiSessionInstallLockout.enabled undefined true
app.update.multiSessionInstallLockout.timeoutMs undefined 345600000
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
apz.popups_without_remote.enabled undefined false
browser.contentblocking.report.vpn_regions 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 as,at,au,bd,be,bg,br,ca,ch,cl,co,cy,cz,de,dk,ee,eg,es,fi,fr,gb,gg,gr,hr,hu,id,ie,im,in,io,it,je,ke,kr,lt,lu,lv,ma,mp,mt,mx,my,ng,nl,no,nz,pl,pr,pt,ro,sa,se,sg,si,sk,sn,th,tr,tw,ua,ug,uk,um,us,vg,vi,vn,za
browser.ml.chat.prompts.4 undefined {"id":"proofread", "l10nId":"genai-prompts-proofread"}
browser.ml.defaultModelMemoryUsage 2 1
browser.navigation.requireUserInteraction false true
browser.newtabpage.activity-stream.discoverystream.sections.blocked undefined
browser.newtabpage.activity-stream.discoverystream.sections.following undefined
browser.newtabpage.activity-stream.discoverystream.sections.personalization.enabled undefined false
browser.newtabpage.activity-stream.newtabAdSize.billboard undefined false
browser.newtabpage.activity-stream.newtabAdSize.billboard.position undefined 3
browser.newtabpage.activity-stream.newtabAdSize.leaderboard undefined false
browser.newtabpage.activity-stream.newtabAdSize.leaderboard.position undefined 3
browser.newtabpage.activity-stream.support.url https://support.mozilla.org/1/firefox/134.0.2/Linux/en-US/new-tab https://support.mozilla.org/1/firefox/135.0/Linux/en-US/new-tab
browser.profiles.sync.allow-danger-merge undefined false
browser.shopping.experience2023.ads.exposure false undefined
browser.shopping.experience2023.shoppingSidebar undefined true
browser.tabs.dragdrop.moveOverThresholdPercent undefined 70
browser.urlbar.unifiedSearchButton.always undefined false
browser.urlbar.weather.uiTreatment undefined 0
captchadetection.actor.enabled undefined false
captchadetection.loglevel undefined Warn
dom.block_multiple_popups true undefined
dom.event.mouse.fractional_coordinates.trusted.enabled undefined false
dom.event.mouse.fractional_coordinates.untrusted.enabled undefined false
dom.event.pointer.fractional_coordinates.enabled undefined true
dom.events.mouse-pointer-boundary.keep-enter-targets-after-over-target-removed false true
dom.forms.always_allow_key_and_focus_events.enabled false true
dom.forms.fieldset_disable_only_descendants.enabled false true
extensions.webcompat-reporter.enabled false true
gfx.canvas.accelerated.cache-items 2048 8192
identity.fxaccounts.toolbar.syncSetup.panelAccessed undefined false
javascript.options.experimental.json_parse_with_source false true
javascript.options.wasm_call_ref_inlining_percent 50 40
javascript.options.wasm_lazy_tiering_for_gc false true
layout.css.moz-user-input.enabled undefined false
layout.forms.reveal-password-context-menu.enabled true undefined
media.ffvpx-hw.enabled undefined false
media.gmp.coder-shutdown-timeout-ms undefined 1000
media.webrtc.codec.video.av1.enabled undefined false
media.webrtc.codec.video.av1.experimental_preferred undefined false
network.cookie.sameSite.laxByDefaultWarningsForBeta undefined false
network.dns.use_override_as_peer_address false undefined
network.http.http3.enable_kyber false true
network.http.idempotencyKey.enabled undefined false
network.http.retry_with_another_half_open undefined false
network.http.throttle.read-interval-ms 500 undefined
network.http.throttle.read-limit-bytes 8000 undefined
network.http.throttle.version 1 undefined
network.socket.attach_mock_network_layer undefined false
nimbus.telemetry.targetingContextEnabled undefined true
permissions.manager.remote.enabled undefined false
places.history.floodingPrevention.enabled false true
privacy.resistFingerprinting.target_video_res 480 1080
reader.colors_menu.enabled true undefined
reader.improved_text_menu.enabled true undefined
remote.events.async.enabled false true
security.mls.enabled undefined false
sidebar.revamp.round-content-area undefined false
signon.firefoxRelay.firstOfferVersionFallback undefined control
toolkit.telemetry.enabled false true
ui.panel.default_level_parent true false
webextensions.storage.sync.enabled true undefined
widget.use-xdg-desktop-portal.native-messaging undefined 0