This is difference between the default preference of Firefox 101.0 beta 3 and one of 100.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 100.0Firefox 101.0 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-browser&utm_campaign=whatsnew https://www.mozilla.org/%LOCALE%/firefox/%VERSION%beta/releasenotes/?utm_source=firefox-browser&utm_medium=firefox-browser&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.cache.offline.enable true false
browser.download.always_ask_before_handling_new_types undefined false
browser.flash-protected-mode-flip.done false undefined
browser.flash-protected-mode-flip.enable false undefined
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.places.snapshots.expiration.days undefined 210
browser.places.snapshots.expiration.userManaged.days undefined 420
browser.snapshots.score.InNavigation 3 undefined
browser.snapshots.score.IsOverlappingVisit 3 undefined
browser.snapshots.source.CommonReferrer undefined 3
browser.snapshots.source.Overlapping undefined 3
browser.startup.upgradeDialog.enabled true false
browser.theme.colorway-closet undefined false
browser.urlbar.quicksuggest.blockingEnabled undefined false
browser.urlbar.quicksuggest.impressionCaps.nonSponsoredEnabled undefined false
browser.urlbar.quicksuggest.impressionCaps.sponsoredEnabled undefined false
canvas.mozgetasfile.enabled false undefined
devtools.debugger.features.skip-pausing true undefined
devtools.inspector.draggable_properties undefined true
dom.block_external_protocol_navigation_from_sandbox undefined false
dom.enable_web_task_scheduling undefined false
dom.forms.datetime-local true undefined
dom.forms.datetime-local.widget true undefined
dom.image-lazy-loading.root-margin.bottom 300.0 100.0
dom.image-lazy-loading.root-margin.bottom.percentage false true
dom.image-lazy-loading.root-margin.left 300.0 100.0
dom.image-lazy-loading.root-margin.left.percentage false true
dom.image-lazy-loading.root-margin.right 300.0 100.0
dom.image-lazy-loading.root-margin.right.percentage false true
dom.image-lazy-loading.root-margin.top 300.0 100.0
dom.image-lazy-loading.root-margin.top.percentage false true
dom.input.dirpicker false undefined
dom.input.showPicker undefined true
dom.ipc.plugins.flash.disable-protected-mode false undefined
dom.ipc.plugins.flash.subprocess.crashreporter.enabled true undefined
dom.origin-trials.test-trial.state undefined 0
dom.webidl.crosscontext_hasinstance.enabled true false
dom.webmidi.enabled false true
dom.window.content.untrusted.enabled true false
dom.window.sidebar.enabled true false
extensions.eventPages.enabled undefined false
extensions.manifestV3.enabled undefined false
extensions.webcompat-reporter.enabled false true
fission.enforceBlocklistedPrefsInSubprocesses undefined false
fission.omitBlocklistedPrefsInSubprocesses undefined false
geo.provider.network.url https://www.googleapis.com/geolocation/v1/geolocate?key=%GOOGLE_LOCATION_SERVICE_API_KEY% https://location.services.mozilla.com/v1/geolocate?key=%MOZILLA_API_KEY%
gfx.canvas.accelerated.profile-cache-miss-ratio undefined 0.66
gfx.canvas.accelerated.profile-fallback-ratio undefined 0.3
gfx.canvas.accelerated.profile-frames undefined 10
html5.inert.enabled false true
javascript.options.wasm_simd_avx false true
javascript.options.wasm_simd_wormhole undefined false
layout.accessiblecaret.magnifier.enabled undefined false
layout.css.constructable-stylesheets.enabled false true
layout.css.prefers-contrast.enabled false true
layout.dynamic-reflow-roots.enabled false true
media.gmp-manager.checkContentSignature undefined true
media.utility-ffmpeg.enabled undefined true
media.utility-ffvpx.enabled undefined true
media.utility-opus.enabled undefined true
media.utility-process.enabled undefined false
media.utility-vorbis.enabled undefined true
media.utility-wav.enabled undefined true
media.video.dropped_frame_stats.enabled undefined true
media.videocontrols.picture-in-picture.audio-toggle.enabled false true
media.videocontrols.picture-in-picture.display-text-tracks.enabled false true
media.videocontrols.picture-in-picture.display-text-tracks.size undefined medium
media.webrtc.platformencoder.sw_mft false true
mozilla.widget.raise-on-setfocus undefined true
network.cache.frecency_array_check_enabled false true
network.cookie.sameSite.laxByDefault false true
network.cookie.sameSite.noneRequiresSecure false true
network.cookie.sameSite.schemeful false true
network.http.http2.websockets true false
network.jar.record_failure_reason false true
network.predictor.enable-prefetch false true
privacy.annotate_channels.strict_list.enabled false true
privacy.restrict3rdpartystorage.expiration_redirect 900 2592000
remote.active-protocols 2 3
remote.force-local true undefined
security.disallow_non_local_systemprincipal_in_tests undefined false
security.intermediate_preloading_healer.enabled false true
security.pki.name_matching_mode 3 undefined
security.remote_settings.crlite_filters.enabled false true
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.passwords.validation.enabled undefined true
toolkit.telemetry.enabled false true
widget.swipe.whole-page-pixel-size undefined 550.0
widget.transparent-windows undefined true
widget.use-xdg-desktop-portal.location undefined 2