This is difference between the default preference of Firefox 81.0 beta 6 and one of 80.0.1. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 80.0.1Firefox 81.0 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.langpack.enabled undefined true
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.one_touch_pinch.enabled true false
browser.aboutwelcome.overrideContent {"id": "multi-stage-welcome-default","template": "multistage","screens": [{"id": "AW_GET_STARTED","order": 0,"content": {"zap": true,"title": {"string_id": "onboarding-multistage-welcome-header"},"subtitle": {"string_id": "onboarding-multistage-welcome-subtitle"},"primary_button": {"label": {"string_id": "onboarding-multistage-welcome-primary-button-label"},"action": {"navigate": true}},"secondary_button": {"text": {"string_id": "onboarding-multistage-welcome-secondary-button-text"},"label": {"string_id": "onboarding-multistage-welcome-secondary-button-label"},"position": "top","action": {"type": "OPEN_URL","addFlowParams": true,"data": {"args": "https://accounts.firefox.com/?service=sync&action=email&context=fx_desktop_v3&entrypoint=activity-stream-firstrun&style=trailhead","where": "current"}}}}}, {"id": "AW_IMPORT_SETTINGS","order": 1,"content": {"zap": true, "disclaimer": {"string_id": "onboarding-import-sites-disclaimer"},"title": {"string_id": "onboarding-multistage-import-header"},"subtitle": {"string_id": "onboarding-multistage-import-subtitle"},"tiles": {"type": "topsites","info": true},"primary_button": {"label": {"string_id": "onboarding-multistage-import-primary-button-label"},"action": {"type": "SHOW_MIGRATION_WIZARD","navigate": true}},"secondary_button": {"label": {"string_id": "onboarding-multistage-import-secondary-button-label"},"action": {"navigate": true}}}}, {"id": "AW_CHOOSE_THEME","order": 2,"content": {"zap": true,"title": {"string_id": "onboarding-multistage-theme-header"},"subtitle": {"string_id": "onboarding-multistage-theme-subtitle"},"tiles": {"type": "theme","action": {"theme": "<event>"}, "data": [{"theme": "automatic","label": {"string_id": "onboarding-multistage-theme-label-automatic"}, "description": {"string_id": "onboarding-multistage-theme-description-automatic"}, "tooltip": {"string_id": "onboarding-multistage-theme-tooltip-automatic"}}, {"theme": "light","label": {"string_id": "onboarding-multistage-theme-label-light"}, "tooltip": {"string_id": "onboarding-multistage-theme-tooltip-light"}},{"theme": "dark","label": {"string_id": "onboarding-multistage-theme-label-dark"}, "tooltip": {"string_id": "onboarding-multistage-theme-tooltip-dark"}}]},"primary_button": {"label": {"string_id": "onboarding-multistage-theme-primary-button-label"},"action": {"navigate": true}},"secondary_button": {"label": {"string_id": "onboarding-multistage-theme-secondary-button-label"},"action": {"theme": "automatic","navigate": true}}}}]}
browser.cache.offline.storage.enable true false
browser.defaultbrowser.notificationbar false true
browser.defaultbrowser.notificationbar.checkcount undefined 0
browser.defaultbrowser.notificationbar.checklimit undefined 10000
browser.download.viewableInternally.enabledTypes undefined xml,svg,webp,avif
browser.helperApps.showOpenOptionForViewableInternally undefined true
browser.migrate.showBookmarksToolbarAfterMigration undefined true
browser.newtabpage.activity-stream.discoverystream.locale-list-config undefined
browser.newtabpage.activity-stream.discoverystream.personalization.version 2 1
browser.newtabpage.activity-stream.discoverystream.region-layout-config US,CA,GB,DE,IE US,CA,GB,DE,IE,CH,AT,BE
browser.newtabpage.activity-stream.discoverystream.region-stories-config US,DE,CA,GB,IE US,DE,CA,GB,IE,CH,AT,BE
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.partnerlink.attributionURL undefined https://topsites.mozilla.io/cid/amzn_2020_a1
browser.tabs.documentchannel true undefined
browser.tabs.documentchannel.parent-initiated true undefined
browser.tabs.documentchannel.ppdc true undefined
devtools.inspector.ruleview.inline-compatibility-warning.enabled undefined false
dom.block_download_in_sandboxed_iframes undefined false
dom.document.exec_command.nested_calls_allowed true false
dom.experimental_forms false undefined
dom.forms.color true undefined
dom.forms.datetime true undefined
dom.security.featurePolicy.enabled true undefined
dom.storage.next_gen false true
dom.webcomponents.elementInternals.enabled false undefined
dom.webcomponents.formAssociatedCustomElement.enabled undefined false
dom.window.content.untrusted.enabled true false
domsecurity.httpsonly.infoURL https://developer.mozilla.org/en-US/docs/Glossary/https undefined
extensions.formautofill.creditCards.available false true
extensions.webcompat-reporter.enabled false true
fission.preserve_browsing_contexts false true
fission.remoteObjectEmbed undefined false
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.capture-profiler undefined false
html5.inert.enabled undefined false
identity.fxaccounts.service.sendLoginUrl https://send.firefox.com/login/ undefined
javascript.options.wasm_simd undefined false
layers.iosurfaceimage.recycle-limit undefined 15
layout.css.comparison-functions.enabled true undefined
layout.css.cross-fade.enabled undefined false
layout.css.forced-colors.enabled undefined false
layout.css.is-where-selectors.enabled true undefined
layout.css.moz-any-is-is.enabled undefined true
layout.css.moz-focus-outer.enabled true false
layout.css.offset-logical-properties.enabled false undefined
layout.css.shadow-parts.enabled true undefined
layout.dynamic-reflow-roots.enabled false true
layout.forms.input-type-search.enabled undefined false
media.ffmpeg.vaapi-drm-display.enabled false true
media.getusermedia.camera.background.mute.enabled undefined false
media.hardwaremediakeys.enabled false true
media.mediacontrol.stopcontrol.aftermediaends undefined true
media.mediacontrol.stopcontrol.timer undefined false
media.peerconnection.dtls.version.min 770 771
media.peerconnection.mtransport_process false true
network.dns.upgrade_with_https_rr undefined false
network.dns.use_https_rr_as_altsvc undefined false
network.http.http3.alt-svc-mapping-for-testing undefined
network.http.http3.default-max-stream-blocked 10 20
network.http.http3.default-qpack-table-size 0 65536
network.preload false true
network.process.enabled false true
network.trr.blocklist_cleanup_done undefined false
network.trr.enable_when_nrpt_detected false undefined
network.trr.enable_when_proxy_detected false undefined
network.trr.enable_when_vpn_detected false undefined
pdfjs.renderInteractiveForms false true
permissions.isolateBy.privateBrowsing false true
print.tab_modal.enabled false true
privacy.annotate_channels.strict_list.enabled false true
privacy.partition.bloburl_per_agent_cluster undefined false
privacy.purge_trackers.enabled false true
privacy.purge_trackers.logging.level Error Warn
prompts.tabChromePromptSubDialog undefined false
security.bad_cert_domain_error.url_fix_enabled false true
security.block_Worker_with_wrong_mime false true
security.disallow_non_local_systemprincipal_in_tests undefined false
security.intermediate_preloading_healer.enabled false true
security.remote_settings.crlite_filters.enabled false true
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.safebrowsing.downloads.enabled undefined true
services.sync.prefs.sync.browser.safebrowsing.downloads.remote.block_potentially_unwanted undefined true
services.sync.prefs.sync.browser.safebrowsing.malware.enabled undefined true
services.sync.prefs.sync.browser.safebrowsing.phishing.enabled undefined true
services.sync.prefs.sync.dom.security.https_only_mode undefined true
services.sync.prefs.sync.dom.security.https_only_mode_ever_enabled undefined true
services.sync.prefs.sync.dom.security.https_only_mode_ever_enabled_pbm undefined true
services.sync.prefs.sync.dom.security.https_only_mode_pbm undefined true
services.sync.prefs.sync.signon.autofillForms undefined true
services.sync.prefs.sync.signon.generation.enabled undefined true
services.sync.prefs.sync.signon.management.page.breach-alerts.enabled undefined true
signon.capture.inputChanges.enabled false true
signon.showAutoCompleteImport import
signon.suggestImportCount undefined 3
toolkit.telemetry.enabled false true
widget.wayland.use-opaque-region true false