This is difference between the default preference of Firefox 99.0 beta 5 and one of 98.0.1. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 98.0.1Firefox 99.0 beta 5
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.contentblocking.report.vpn.enabled true undefined
browser.contentblocking.report.vpn_regions us,ca,nz,sg,my,gb,de,fr at,be,ca,ch,de,fr,ie,it,my,nl,nz,sg,es,gb,us
browser.newtabpage.activity-stream.asrouter.disable-captive-portal-vpn-promo false undefined
browser.newtabpage.activity-stream.discoverystream.readTime.enabled false true
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.soft_reload.only_force_validate_top_level_document false true
browser.urlbar.bestMatch.blockingEnabled undefined false
browser.urlbar.bestMatch.enabled true false
browser.urlbar.suggest.bestmatch undefined true
devtools.inspector.selectedSidebar undefined layoutview
devtools.netmonitor.customRequest undefined {}
docshell.shistory.bfcache.ship_allow_beforeunload_listeners undefined false
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.script_loader.delazification.max_size undefined 10485760
dom.script_loader.delazification.min_mem undefined 2
dom.script_loader.delazification.strategy undefined 255
dom.script_loader.full_parse_max_size 10485760 undefined
dom.script_loader.full_parse_min_mem 2 undefined
dom.serviceWorkers.navigationPreload.enabled false true
dom.streams.pipeTo.enabled undefined false
dom.streams.transform_streams.enabled undefined false
dom.webmidi.enabled false true
dom.window.content.untrusted.enabled true false
dom.window.sidebar.enabled true false
dom.workers.requestAnimationFrame false true
editor.create_element_transaction.enabled false undefined
extensions.formautofill.addresses.supported undefined detect
extensions.formautofill.addresses.supportedCountries undefined US,CA
extensions.formautofill.creditCards.supported undefined detect
extensions.formautofill.creditCards.supportedCountries undefined US,CA,UK,FR,DE
extensions.formautofill.supportedCountries US,CA undefined
extensions.pocket.refresh.hideRecentSaves.enabled undefined false
extensions.webcompat-reporter.enabled false true
extensions.webextensions.background-delayed-startup true undefined
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.cache-items 1024 2048
gfx.canvas.accelerated.cache-size 128 256
gfx.offscreencanvas.domain-allowlist *.zoom.us
gfx.offscreencanvas.domain-enabled false true
gfx.will-change.ignore-opacity false true
intl.multilingual.aboutWelcome.languageMismatchEnabled undefined false
javascript.options.wasm_simd_wormhole undefined false
javascript.options.watchtower.megamorphic undefined true
layout.css.grid-item-baxis-measurement.enabled false true
layout.css.scrollbar-width-thin.disabled undefined false
layout.dynamic-reflow-roots.enabled false true
media.audio.audiosink.threshold_ms 1000.0 200.0
media.gmp-manager.checkContentSignature undefined true
media.peerconnection.mtransport_process false true
media.peerconnection.rtpsourcesapi.enabled true undefined
media.videocontrols.picture-in-picture.display-text-tracks.enabled undefined false
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.encoding.trustworthy_is_https undefined true
network.http.referer.disallowCrossSiteRelaxingDefault false true
network.http.useragent.forceVersion undefined 0
network.jar.record_failure_reason false true
network.max_socket_process_failed_count undefined 1
network.predictor.enable-prefetch false true
network.process.enabled false true
network.trr.strict_fallback_request_timeout_ms undefined 6000
network.trr.strict_native_fallback_allow_timeouts undefined true
privacy.annotate_channels.strict_list.enabled false true
reader.color_scheme light auto
reader.color_scheme.values ["light","dark","sepia"] ["light","dark","sepia","auto"]
reader.improvements_H12022.enabled undefined false
security.csp.enable true undefined
security.disallow_non_local_systemprincipal_in_tests undefined false
security.intermediate_preloading_healer.enabled false true
security.remote_settings.crlite_filters.enabled false true
security.sandbox.content.headless false true
security.sandbox.content.win32k-disable false undefined
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.passwords.validation.enabled undefined true
services.sync.engine.tabs.filteredSchemes undefined about|resource|chrome|file|blob|moz-extension
services.sync.engine.tabs.filteredUrls ^(about:.*|resource:.*|chrome:.*|file:.*|blob:.*|moz-extension:.*)$ undefined
services.sync.syncedTabs.syncDelayAfterTabChange undefined 0
signon.usernameOnlyForm.lookupThreshold undefined 5
svg.use-element.graphics-element-restrictions undefined 1
toolkit.telemetry.enabled false true
webgl.out-of-process false true
widget.gtk.alt-theme.scrollbar false undefined
widget.gtk.file-manager-show-items-timeout-ms undefined 1000
widget.gtk.native-context-menus undefined false
widget.gtk.overlay-scrollbars.enabled undefined true
widget.gtk.theme-scrollbar-colors.enabled undefined true
widget.non-native-theme.scrollbar.dark-themed undefined true
widget.swipe.success-threshold undefined 0.25
widget.swipe.success-velocity-contribution undefined 0.05
widget.swipe.velocity-twitch-tolerance undefined 1e-7
widget.use-xdg-desktop-portal.print 0 undefined
widget.wayland.use-move-to-rect undefined true