This is difference between the default preference of Firefox 82.0 beta 6 and one of 81.0.1. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 81.0.1Firefox 82.0 beta 6
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.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
browser.cache.offline.storage.enable true false
browser.defaultbrowser.notificationbar false true
browser.migrate.showBookmarksToolbarAfterMigration false true
browser.newtabpage.activity-stream.asrouter.providers.cfr {"id":"cfr","enabled":true,"type":"remote-settings","bucket":"cfr","frequency":{"custom":[{"period":"daily","cap":1}]},"categories":["cfrAddons","cfrFeatures"],"updateCycleInMs":3600000} {"id":"cfr","enabled":true,"type":"remote-settings","bucket":"cfr","updateCycleInMs":3600000}
browser.newtabpage.activity-stream.asrouter.providers.cfr-fxa {"id":"cfr-fxa","enabled":true,"type":"remote-settings","bucket":"cfr-fxa","frequency":{"custom":[{"period":"daily","cap":1}]},"updateCycleInMs":3600000} {"id":"cfr-fxa","enabled":true,"type":"remote-settings","bucket":"cfr-fxa","updateCycleInMs":3600000}
browser.newtabpage.activity-stream.discoverystream.region-stories-block undefined FR
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.search.geoSpecificDefaults true undefined
browser.search.geoSpecificDefaults.url https://search.services.mozilla.com/1/%APP%/%VERSION%/%CHANNEL%/%LOCALE%/%REGION%/%DISTRIBUTION%/%DISTRIBUTION_VERSION% undefined
browser.search.modernConfig true undefined
browser.urlbar.update2.disableOneOffsHorizontalKeyNavigation undefined false
browser.urlbar.update2.emptySearchBehavior undefined 2
devtools.netmonitor.features.serverSentEvents false true
devtools.whatsnew.enabled false undefined
devtools.whatsnew.feature-enabled false undefined
dom.block_download_in_sandboxed_iframes false true
dom.disable_window_open_feature.close false undefined
dom.disable_window_open_feature.location true undefined
dom.disable_window_open_feature.menubar false undefined
dom.disable_window_open_feature.minimizable false undefined
dom.disable_window_open_feature.personalbar false undefined
dom.disable_window_open_feature.resizable true undefined
dom.disable_window_open_feature.status true undefined
dom.disable_window_open_feature.titlebar false undefined
dom.disable_window_open_feature.toolbar false undefined
dom.document.exec_command.nested_calls_allowed true false
dom.max_script_run_time_without_important_user_input undefined 10
dom.media.mediasession.enabled false true
dom.media.silence_duration_for_audibility undefined 2.0
dom.min_background_timeout_value_without_budget_throttling undefined 1000
dom.script_loader.external_scripts.speculative_omt_parse.enabled false true
dom.security.https_only_mode_send_http_background_request undefined true
dom.security.sanitizer.enabled undefined false
dom.storage.next_gen false true
dom.window.content.untrusted.enabled true false
editor.hr_element.allow_to_delete_from_following_line undefined false
extensions.formautofill.creditCards.available false true
extensions.formautofill.creditCards.enabled false true
extensions.pocket.onSaveRecs undefined false
extensions.pocket.onSaveRecs.locales undefined en-US,en-GB,en-CA
extensions.postDownloadThirdPartyPrompt undefined true
extensions.webcompat-reporter.enabled false true
general.smoothScroll.mouseWheel.durationMaxMS 400 200
general.smoothScroll.mouseWheel.durationMinMS 200 50
general.smoothScroll.mouseWheel.migrationPercent undefined 100
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.webrender.debug.disable-raster-root-scale false undefined
javascript.options.mem.gc_helper_thread_ratio undefined 50
javascript.options.mem.gc_max_helper_threads undefined 8
javascript.options.off_thread_parse_global undefined true
layout.css.counter-ancestor-scope.enabled undefined true
layout.css.file-chooser-button.enabled false undefined
layout.css.file-selector-button.enabled undefined true
layout.css.is-and-where-better-error-recovery.enabled undefined true
layout.css.moz-any-is-is.enabled false true
layout.dynamic-reflow-roots.enabled false true
mathml.legacy_number_syntax.disabled true undefined
mathml.nonzero_unitless_lengths.disabled true undefined
media.clockdrift.buffering 5 50
media.ffmpeg.low-latency.enabled false undefined
media.navigator.video.offer_rtcp_rsize undefined true
media.peerconnection.dtls.version.min 770 771
media.peerconnection.mtransport_process false true
media.videocontrols.picture-in-picture.video-toggle.mode -1 2
network.preload false true
network.process.enabled false true
network.trr.split_horizon_mitigations undefined true
pdfjs.renderInteractiveForms false true
permissions.isolateBy.privateBrowsing false true
print.default_dpi undefined 144.0
print.tab_modal.enabled false true
privacy.annotate_channels.strict_list.enabled false true
privacy.purge_trackers.enabled false true
privacy.purge_trackers.logging.level Error Warn
privacy.window.name.update.enabled undefined false
prompts.modalType.httpAuth undefined 3
prompts.tabChromePromptSubDialog false true
security.bad_cert_domain_error.url_fix_enabled false true
security.caps.allow_uri_is_ui_resource_in_checkloaduriflags undefined false
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.view-source.reachable-from-inner-protocol false undefined
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.creditcards.available false true
services.sync.engine.passwords.validation.enabled undefined true
services.sync.prefs.sync.browser.newtabpage.activity-stream.asrouter.userprefs.cfr.addons undefined true
services.sync.prefs.sync.browser.newtabpage.activity-stream.asrouter.userprefs.cfr.features undefined true
services.sync.prefs.sync.browser.sessionstore.warnOnQuit undefined true
services.sync.prefs.sync.browser.urlbar.suggest.topsites undefined true
services.sync.prefs.sync.general.autoScroll undefined true
services.sync.prefs.sync.general.smoothScroll undefined true
services.sync.prefs.sync.media.videocontrols.picture-in-picture.video-toggle.enabled undefined true
services.sync.prefs.sync.privacy.userContext.enabled undefined true
services.sync.prefs.sync.privacy.userContext.newTabContainerOnLeftClick.enabled undefined true
services.sync.prefs.sync.ui.osk.enabled undefined true
toolkit.aboutProcesses.showAllSubframes undefined false
toolkit.aboutProcesses.showThreads undefined false
toolkit.telemetry.enabled false true
trailhead.firstrun.branches join-dynamic undefined
trailhead.firstrun.newtab.triplets undefined
webgl.enable-ahardwarebuffer undefined false
webgl.out-of-process.shmem-size undefined 100000