This is difference between the default preference of Firefox 90.0 beta 3 and one of 89.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 89.0Firefox 90.0 beta 3
accessibility.cache.enabled undefined false
advanced.mailftp false undefined
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/ https://www.mozilla.org/%LOCALE%/firefox/beta
browser.aboutwelcome.protonDesign undefined true
browser.cache.offline.enable true false
browser.cache.offline.storage.enable false undefined
browser.download.improvements_to_download_panel undefined false
browser.download.viewableInternally.enabledTypes xml,svg,webp,avif xml,svg,webp,avif,jxl
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.topsites.contile.enabled undefined false
browser.topsites.contile.endpoint undefined https://contile.services.mozilla.com/v1/tiles
browser.urlbar.quicksuggest.nonSponsoredIndex undefined -1
browser.urlbar.quicksuggest.sponsoredIndex undefined -1
browser.urlbar.unitConversion.enabled undefined false
canvas.createConicGradient.enabled false true
dom.event.wheelDelta.enabled undefined true
dom.events.asyncClipboard.read undefined false
dom.image-lazy-loading.root-margin.bottom 300.0 600.0
dom.image-lazy-loading.root-margin.left 300.0 600.0
dom.image-lazy-loading.root-margin.right 300.0 600.0
dom.image-lazy-loading.root-margin.top 300.0 600.0
dom.mouse_capture.enabled undefined true
dom.quotaManager.caching.checkBuildId undefined true
dom.security.https_first undefined false
dom.security.https_first_pbm undefined false
dom.security.https_only_mode_https_first false undefined
dom.security.https_only_mode_https_first_pbm false undefined
dom.security.secFetch.enabled false true
dom.storage.next_gen false true
dom.w3c_pointer_events.implicit_capture false true
dom.webnotifications.silent.enabled undefined false
dom.webnotifications.vibrate.enabled undefined false
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.font-list-omt.enabled undefined false
gfx.webrender.fallback.basic true false
gfx.webrender.software.unaccelerated-widget.allow false true
image.avif.compliance_strictness undefined 1
image.exif-density-correction.enabled undefined true
image.exif-density-correction.sanity-check.enabled undefined true
image.jxl.enabled undefined false
image.svg.blob-image undefined false
intl.charset.detector.ng.in.enabled false true
intl.charset.detector.ng.jp.enabled false true
intl.charset.detector.ng.lk.enabled false true
intl.ime.use_composition_events_for_insert_text undefined false
javascript.options.concurrent_multiprocess_gcs.cpu_divisor undefined 4
javascript.options.concurrent_multiprocess_gcs.max undefined 0
javascript.options.experimental.ergonomic_brand_checks undefined true
javascript.options.experimental.private_fields undefined true
javascript.options.experimental.private_methods undefined true
javascript.options.self_hosted.use_shared_memory undefined true
javascript.options.wasm_simd_wormhole undefined false
layout.css.accent-color.enabled undefined false
layout.css.moz-control-character-visibility.enabled undefined false
layout.css.ruby.position-alternate.enabled true undefined
layout.dynamic-reflow-roots.enabled false true
layout.extra-tick.minimum-ms undefined -1
layout.keep_ticking_after_load_ms undefined 1000
media.mediacontrol.stopcontrol.timer false true
media.mediacontrol.stopcontrol.timer.ms 60000 86400000
media.peerconnection.mtransport_process false true
media.useAudioChannelAPI false undefined
mousewheel.system_scroll_override.enabled undefined false
mousewheel.system_scroll_override.horizontal.factor undefined 200
mousewheel.system_scroll_override.vertical.factor undefined 200
mousewheel.system_scroll_override_on_root_content.enabled false undefined
mousewheel.system_scroll_override_on_root_content.horizontal.factor 200 undefined
mousewheel.system_scroll_override_on_root_content.vertical.factor 200 undefined
network.cache.frecency_array_check_enabled false true
network.dns.negative_ttl_for_type_record undefined 300
network.dns.upgrade_with_https_rr false true
network.dns.use_https_rr_as_altsvc false true
network.ftp.control.qos 0 undefined
network.ftp.data.qos 0 undefined
network.ftp.enabled false undefined
network.ftp.idleConnectionTimeout 300 undefined
network.http.http3.enabled false true
network.http.http3.support_version1 undefined true
network.jar.record_failure_reason false true
network.process.enabled false true
network.proxy.ftp undefined
network.proxy.ftp_port 0 undefined
nimbus.debug undefined false
pdfjs.enableWebGL false undefined
pdfjs.enableXfa undefined false
pdfjs.renderer canvas undefined
places.forgetThisSite.clearByBaseDomain undefined false
plugin.mousewheel.enabled true undefined
print.save_as_pdf.links.enabled undefined true
privacy.annotate_channels.strict_list.enabled false true
privacy.query_stripping.allow_list undefined
privacy.query_stripping.enabled undefined false
privacy.query_stripping.redirect undefined true
privacy.query_stripping.strip_list undefined
privacy.resistFingerprinting.exemptedDomains undefined *.example.invalid
privacy.resistFingerprinting.testGranularityMask undefined 0
remote.enabled true undefined
security.disallow_non_local_systemprincipal_in_tests undefined false
security.intermediate_preloading_healer.enabled false true
security.osclientcerts.autoload false true
security.remote_settings.crlite_filters.enabled false true
security.sandbox.content.win32k-disable undefined false
services.blocklist.pinning.bucket pinning undefined
services.blocklist.pinning.checked 0 undefined
services.blocklist.pinning.collection pins undefined
services.blocklist.pinning.enabled true undefined
services.blocklist.pinning.signer pinning-preload.content-signature.mozilla.org undefined
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.passwords.validation.enabled undefined true
services.sync.engine.tabs.filteredUrls ^(about:.*|resource:.*|chrome:.*|wyciwyg:.*|file:.*|blob:.*|moz-extension:.*)$ ^(about:.*|resource:.*|chrome:.*|file:.*|blob:.*|moz-extension:.*)$
threads.control_event_queue.enabled undefined true
toolkit.backgroundtasks.defaultTimeoutSec undefined 600
toolkit.telemetry.enabled false true
ui.android.mouse_as_touch 1 undefined
widget.content.allow-gtk-dark-theme.accent true undefined
widget.content.allow-gtk-dark-theme.scrollbar false undefined
widget.content.allow-gtk-dark-theme.scrollbar_active true undefined
widget.content.allow-gtk-dark-theme.selection true undefined
widget.gtk.alt-theme.accent undefined true
widget.gtk.alt-theme.dark undefined false
widget.gtk.alt-theme.scrollbar undefined false
widget.gtk.alt-theme.scrollbar_active undefined true
widget.gtk.alt-theme.selection undefined true
widget.system-colors-follow-theme undefined false
widget.wayland.fractional_buffer_scale undefined 0.0
widget.wayland.vsync.enabled undefined true
widget.wayland_vsync.enabled true undefined