This article shows the difference between the default preferences of Firefox 150.0 beta 10 and Firefox 149.0.2. The diff table below is generated using my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 150.0 beta 10Firefox 149.0.2
accessibility.ariaNotify.enabled false true
app.releaseNotesURL https://www.mozilla.org/%LOCALE%/firefox/%VERSION%/releasenotes/?utm_source=firefox-browser&utm_medium=firefox-desktop&utm_campaign=whatsnew https://www.mozilla.org/%LOCALE%/firefox/%VERSION%beta/releasenotes/?utm_source=firefox-browser&utm_medium=firefox-desktop&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/new?reason=manual-update https://www.mozilla.org/%LOCALE%/firefox/beta?reason=manual-update
browser.ai.control.smartWindow undefined default
browser.backup.enabled_on.profiles undefined {}
browser.contentblocking.report.privacy_metrics.enabled undefined false
browser.design-tokens.nova undefined false
browser.firefox-view.button-clicks undefined {"count":0,"lastCountTime":""}
browser.firefox-view.view-count 0 undefined
browser.ipProtection.bandwidthWarningDismissedThreshold undefined 0
browser.newtabpage.activity-stream.discoverystream.sections.locale-content-config en-US,en-CA en-US,en-CA,en-GB
browser.newtabpage.activity-stream.discoverystream.sections.region-content-config US US,GB,CA,IE
browser.newtabpage.activity-stream.externalComponents.enabled true undefined
browser.newtabpage.activity-stream.feeds.sectionslayoutfeed undefined true
browser.newtabpage.activity-stream.nova.enabled undefined false
browser.newtabpage.activity-stream.privacyInfo.url https://support.mozilla.org/1/firefox/149.0.2/Linux/en-US/sponsor-privacy https://support.mozilla.org/1/firefox/150.0/Linux/en-US/sponsor-privacy
browser.newtabpage.activity-stream.search.useHandoffComponent true undefined
browser.newtabpage.activity-stream.selfLoading.enabled false true
browser.newtabpage.activity-stream.support.url https://support.mozilla.org/1/firefox/149.0.2/Linux/en-US/new-tab https://support.mozilla.org/1/firefox/150.0/Linux/en-US/new-tab
browser.newtabpage.activity-stream.topSitesMaxSitesPerRow undefined 8
browser.newtabpage.activity-stream.unifiedAds.ohttp.enabled false true
browser.newtabpage.activity-stream.weather.display simple detailed
browser.newtabpage.activity-stream.weather.hourlyEndpoint undefined https://merino.services.mozilla.com/api/v1/weather/hourly-forecasts
browser.newtabpage.activity-stream.weather.reportEndpoint undefined https://merino.services.mozilla.com/api/v1/suggest
browser.newtabpage.activity-stream.widgets.feedback.enabled undefined false
browser.newtabpage.activity-stream.widgets.hideAllToast.enabled undefined false
browser.profiles.enabled false true
browser.profiles.forceEnableRefresh false undefined
browser.safebrowsing.realTime.simulation.hitProbability 100 5
browser.safebrowsing.realTime.simulation.negativeCacheEnabled undefined false
browser.safebrowsing.realTime.simulation.negativeCacheTTLSec undefined 300
browser.shareqrcode.enabled undefined false
browser.smartwindow.conversation.logLevel undefined Error
browser.smartwindow.firstrun.explainerURL undefined https://www.firefox.com/en-US/smart-window/?v=product
browser.smartwindow.memories true undefined
browser.smartwindow.memories.generateFromConversation undefined true
browser.smartwindow.memories.generateFromHistory undefined true
browser.smartwindow.memories.hasSeenMemories undefined false
browser.smartwindow.showThemesNotice undefined true
browser.smartwindow.sidebar.openByDefault undefined true
browser.tabs.dragDrop.createGroup.enabled undefined true
browser.tabs.groups.alternateMenu undefined false
browser.translations.quickAction.enabled false true
browser.urlbar.autoFill.adaptiveHistory.backspaceBlockDurationMs undefined 172800000
browser.urlbar.autoFill.adaptiveHistory.dismissalBlockDurationMs undefined 604800000
browser.urlbar.merino.ohttpConfigURL https://ohttp-gateway-merino.services.mozilla.com/ohttp-configs
browser.urlbar.merino.ohttpRelayURL https://ohttp-merino.mozilla.fastly-edge.com
browser.urlbar.merino.timeoutMs 200 500
browser.urlbar.merino.weather.hourlyEndpointURL undefined https://merino.services.mozilla.com/api/v1/weather/hourly-forecasts
browser.urlbar.merino.weather.reportEndpointURL undefined https://merino.services.mozilla.com/api/v1/suggest
browser.urlbar.nova.featureGate undefined false
browser.urlbar.perplexity.hasBeenInSearchMode false undefined
devtools.inspector.remote false undefined
docshell.shistory.testing.bfevict false undefined
dom.caretRangeFromPoint.enabled undefined true
dom.event.wheel-event-groups.enabled true undefined
dom.keyboardevent.init_key_event.enabled_in_addons false undefined
dom.lift_select_parser_restrictions.enabled undefined false
dom.media.pseudo-classes.enabled false true
dom.modelcontext.enabled undefined false
dom.modelcontext.testing.enabled undefined false
dom.movebefore.enabled true undefined
dom.multiple_import_maps.enabled undefined false
dom.scoped-custom-element-registries.enabled undefined false
dom.shadowdom.new_caretPositionFromPoint_behavior.enabled false true
dom.tcpsocket_in_child.enabled undefined false
editor.htmleditor.inputevent.hack.no_dispatch_after_compositionend www.icloud.com
extensions.webcompat-reporter.enabled false true
fission.disableSessionHistoryInParent false undefined
gfx.font_rendering.freetype.enhanced_contrast undefined 0
gfx.font_rendering.freetype.gamma undefined -1
gfx.webrender.enable-item-cache true false
gfx.webrender.precise-linear-gradients false true
javascript.options.batch_microtask_execution undefined true
javascript.options.wasm_wide_arithmetic undefined false
layout.css.appearance-base.enabled undefined false
layout.css.color-mix-multi-color.enabled false true
layout.css.light-dark.images.enabled false true
layout.css.revert-rule.enabled undefined true
mathml.lspace_rspace_for_child_spacing_during_mrow_layout.enabled undefined false
media.devices.enumerate.legacy.allowlist slack.com,*.slack.com,riverside.fm,*.riverside.fm slack.com,*.slack.com,riverside.fm,*.riverside.fm,riverside.com,*.riverside.com
media.eme.mediadrm.origin-id.enabled undefined false
media.gmp.coder-shutdown-timeout-ms 1000 undefined
memory.lazypurge.minimum_idle_budget 5 10
network.cookie.CHIPS.affectsTCP undefined false
network.http.happy_eyeballs_enabled undefined false
network.http.http3.slow_start_algorithm undefined 0
network.http.rcwn.race_with_non_ssd true false
network.http_index_format.allowed_schemes file,moz-gio file
network.lna.block_insecure_contexts undefined true
network.lna.temporary_permission_expire_time_ms undefined 86400000
network.tcp.notsent_lowat undefined 0
network.tcp.user_timeout undefined 0
network.trr.fast_pto_for_http3_conn undefined 0
network.trr.skip-AAAA-when-not-supported true undefined
network.trr.useGET false true
network.trr.wait-for-portal false undefined
pdfjs.enableNewBadge undefined true
pdfjs.enableSplitMerge false true
pdfjs.imagesRightClickMinSize undefined 16
permissions.default.localhost 0 undefined
permissions.default.loopback-network undefined 0
permissions.expireUnused.enabled undefined false
permissions.expireUnusedThresholdSec undefined 33696000
permissions.expireUnusedTypes undefined autoplay-media,cookie,camera,localhost,local-network,microphone,screen,speaker,popup,install,geo,open-protocol-handler^,xr,focus-tab-by-prompt,shortcuts,canvas,midi,midi-sysex,storage-access,3rdPartyStorage^,3rdPartyFrameStorage^
privacy.reducePageProtection.infobar.enabled.pbmode undefined false
security.utility_pkcs11_module_process.enabled undefined false
security.waict.allowed_image_storage undefined 52428800
security.waict.downgrade_protection.enable undefined false
security.waict.enabled undefined false
sidebar.history.sortOption undefined date
signon.firefoxRelay.firstOfferVersionFallback control undefined
toolkit.telemetry.enabled false true
webgl.allow-in-parent undefined true
webgl.ignore-blocklist undefined false
widget.gtk.native-emoji-dialog undefined true
widget.wayland.force-move-to-rect false undefined