This is difference between the default preference of Firefox 85.0 beta 3 and one of 84.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 84.0Firefox 85.0 beta 3
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 undefined 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/ https://www.mozilla.org/%LOCALE%/firefox/beta
apz.relative-update.enabled true undefined
browser.contentblocking.features.strict tp,tpPrivate,cookieBehavior4,cm,fp,stp tp,tpPrivate,cookieBehavior4,cm,fp,stp,lvl2
browser.defaultbrowser.notificationbar false true
browser.display.always_show_rings_after_key_focus undefined false
browser.engagement.downloads-button.has-used undefined false
browser.engagement.fxa-toolbar-menu-button.has-used undefined false
browser.engagement.home-button.has-used undefined false
browser.engagement.sidebar-button.has-used undefined false
browser.fixup.alternate.protocol undefined https
browser.newtabpage.activity-stream.customizationMenu.enabled undefined false
browser.newtabpage.activity-stream.improvesearch.topSiteSearchShortcuts.searchEngines google,amazon
browser.newtabpage.activity-stream.newNewtabExperience.enabled undefined false
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.proton.enabled undefined false
browser.tabs.tooltipsShowPid undefined false
browser.toolbars.bookmarks.2h2020 false true
browser.toolbars.bookmarks.showOtherBookmarks undefined true
browser.urlbar.imeCompositionClosesPanel undefined true
browser.urlbar.shortcuts.bookmarks undefined true
browser.urlbar.shortcuts.history undefined true
browser.urlbar.shortcuts.tabs undefined true
browser.urlbar.suggest.engines undefined true
browser.urlbar.update2.localOneOffs true undefined
browser.urlbar.update2.tabToComplete true undefined
devtools.debugger.features.watchpoints true undefined
devtools.storage.test.forceLegacyActors undefined false
dom.delay.block_external_protocol_in_iframes.enabled undefined true
dom.input_events.beforeinput.enabled false true
dom.menuitem.enabled undefined false
dom.storage.next_gen false true
dom.window.content.untrusted.enabled true false
extensions.webcompat-reporter.enabled false true
geo.provider.network.compare.url undefined https://www.googleapis.com/geolocation/v1/geolocate?key=%GOOGLE_LOCATION_SERVICE_API_KEY%
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.e10s.font-list.shared false true
gfx.webrender.allow-partial-present-buffer-age undefined true
javascript.options.warp true undefined
layout.css.conic-gradient.enabled true undefined
layout.css.focus-visible.enabled false true
layout.display-list.improve-fragmentation false true
layout.dynamic-reflow-roots.enabled false true
media.peerconnection.dtls.version.min 770 771
media.peerconnection.mtransport_process false true
media.rdd-ffvpx.enabled false true
media.rdd-retryonfailure.enabled undefined true
media.rdd-theora.enabled false true
media.rdd-vpx.enabled false true
messaging-system.rsexperimentloader.collection_id undefined nimbus-desktop-experiments
network.http.accept undefined
network.http.http3.backup_timer_delay undefined 100
network.preload false true
network.process.enabled false true
network.security.esni.enabled false undefined
permissions.isolateBy.privateBrowsing false true
print.pages_per_sheet.enabled undefined true
print.tab_modal.enabled false true
privacy.annotate_channels.strict_list.enabled false true
privacy.partition.network_state false true
privacy.restrict3rdpartystorage.partitionedHosts accounts.google.com/o/oauth2/ accounts.google.com/o/oauth2/,d35nw2lg0ahg0v.cloudfront.net/,datastudio.google.com/embed/reporting/,d3qlaywcwingl6.cloudfront.net/
security.disallow_non_local_systemprincipal_in_tests undefined false
security.intermediate_preloading_healer.enabled false true
security.pki.distrust_ca_policy 2 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
services.sync.prefs.sync.browser.urlbar.suggest.engines undefined true
toolkit.telemetry.enabled false true
toolkit.zoomManager.zoomValues .3,.5,.67,.8,.9,1,1.1,1.2,1.33,1.5,1.7,2,2.4,3 .3,.5,.67,.8,.9,1,1.1,1.2,1.33,1.5,1.7,2,2.4,3,4,5
widget.titlebar-x11-use-shape-mask undefined false
zoom.maxPercent 300 500