This is difference between the default preference of Firefox 80.0 beta 7 and one of 79.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 79.0Firefox 80.0 beta 7
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
apz.force_disable_desktop_zooming_scrollbars undefined true
apz.mvm.force-enabled false true
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.newtabpage.activity-stream.discoverystream.personalization.version 1 2
browser.newtabpage.activity-stream.discoverystream.region-layout-config US,CA,GB,DE US,CA,GB,DE,IE
browser.newtabpage.activity-stream.discoverystream.region-stories-config US,DE,CA,GB US,DE,CA,GB,IE
browser.preferences.experimental.hidden undefined false
browser.preferences.exposeHTTPSOnly undefined false
browser.region.update.enabled undefined true
browser.tabs.documentchannel.parent-controlled undefined false
browser.topsites.useRemoteSetting undefined false
browser.urlbar.loglevel undefined Error
browser.urlbar.update2 undefined false
browser.urlbar.update2.expandTextOnFocus false undefined
browser.urlbar.update2.localOneOffs undefined false
browser.urlbar.update2.oneOffsRefresh undefined false
browser.urlbar.update2.tabToComplete undefined false
devtools.accessibility.auto-init.enabled true undefined
devtools.netmonitor.audits.slow undefined 500
devtools.responsive.browserUI.enabled true undefined
dom.animations-api.compositing.enabled false true
dom.arena_allocator.enabled false true
dom.block_download_insecure undefined false
dom.max_chrome_script_run_time 20 0
dom.security.https_only_mode_ever_enabled_pbm undefined false
dom.security.https_only_mode_pbm undefined false
dom.security.unexpected_system_load_telemetry_enabled undefined true
dom.sidebar.enabled false undefined
dom.suspend_inactive.enabled undefined false
domsecurity.httpsonly.infoURL undefined https://developer.mozilla.org/en-US/docs/Glossary/https
extensions.backgroundServiceWorker.enabled undefined false
extensions.blocklist.useMLBF false true
extensions.blocklist.useMLBF.stashes false true
extensions.formautofill.addresses.capture.enabled undefined false
extensions.formautofill.creditCards.hideui undefined false
extensions.serviceWorkerRegister.allowed undefined false
extensions.webcompat-reporter.enabled false true
fission.processOriginNames undefined false
gfx.use-ahardwarebuffer-content undefined false
identity.sync.useOAuthForSyncToken false true
layers.gpu-process.enabled true false
layout.animation.prerender.partial.jank undefined false
layout.css.prefers-contrast.enabled undefined false
layout.viewport_contains_no_contents_area true undefined
media.ffmpeg.dmabuf-textures.enabled undefined false
media.ffmpeg.vaapi-drm-display.enabled undefined false
media.ffmpeg.vaapi.enabled undefined false
media.getusermedia.experimental_input_processing false undefined
media.navigator.video.use_transport_cc false true
media.peerconnection.video.use_rtx false true
media.peerconnection.video.use_rtx.blocklist *.google.com
media.videocontrols.picture-in-picture.video-toggle.has-used undefined false
media.videocontrols.picture-in-picture.video-toggle.mode undefined -1
media.videocontrols.picture-in-picture.video-toggle.position undefined right
network.standard-url.punycode-host true undefined
print.tab_modal.enabled undefined false
security.allow_disjointed_external_uri_loads true false
security.bad_cert_domain_error.url_fix_enabled undefined false
security.sandbox.content.headless undefined false
security.ssl3.rsa_aes_128_gcm_sha256 undefined true
security.ssl3.rsa_aes_256_gcm_sha384 undefined true
security.warn_submit_secure_to_insecure undefined true
security.xfocsp.errorReporting.automatic undefined false
security.xfocsp.errorReporting.enabled undefined true
signon.backup.enabled false true
signon.capture.inputChanges.enabled true false
signon.management.page.fileImport.enabled undefined false
storage.sqlite.exclusiveLock.enabled undefined true
toolkit.telemetry.enabled false true
webgl.debug.incomplete-tex-color undefined 0
webgl.oop.via-pcq undefined false
webgl.prototype.ipc-pcq 0 undefined
widget.disable-workspace-management undefined false
widget.dmabuf-webgl.enabled undefined true
widget.wayland-dmabuf-vaapi.enabled false undefined
widget.wayland-dmabuf-video-textures.enabled false undefined
widget.wayland-dmabuf-webgl.enabled true undefined