This is difference between the default preference of Firefox 124.0 beta 7 and one of 123.0.1. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 123.0.1Firefox 124.0 beta 7
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.contentanalysis.default_allow undefined false
browser.newtabpage.activity-stream.discoverystream.ctaButtonSponsors undefined
browser.newtabpage.activity-stream.discoverystream.ctaButtonVariant undefined
browser.opaqueResponseBlocking.syntheticBrowsingContext true undefined
browser.opaqueResponseBlocking.syntheticBrowsingContext.filter true undefined
browser.search.widget.removeAfterDaysUnused undefined 120
browser.tabs.remote.autostart true undefined
browser.urlbar.quicksuggest.rustEnabled false true
browser.urlbar.yelp.featureGate undefined false
browser.urlbar.yelp.minKeywordLength undefined 5
browser.urlbar.yelp.priority undefined false
browser.urlbar.yelp.suggestedIndex undefined 0
devtools.debugger.features.codemirror-next undefined false
dom.animations-api.getAnimations.enabled true undefined
dom.animations.mainthread-synchronization-with-geometric-animations false undefined
dom.domrequest.enabled undefined false
dom.element.blocking.enabled undefined false
dom.event.default_to_passive_wheel_listeners true undefined
dom.events.mouse-pointer-boundary.keep-enter-targets-after-over-target-removed undefined false
dom.events.phases.correctOrderOnTarget true undefined
dom.forms.always_allow_pointer_events.enabled false true
dom.screenwakelock.enabled false true
dom.screenwakelock.testing false undefined
extensions.formautofill.addresses.capture.v2.enabled false undefined
extensions.formautofill.addresses.experiments.enabled undefined false
extensions.formautofill.heuristics.captureOnFormRemoval false true
extensions.formautofill.heuristics.captureOnPageNavigation false true
extensions.webcompat-reporter.enabled false true
gfx.offscreencanvas.shared-provider undefined true
javascript.options.mem.gc_parallel_marking false true
javascript.options.tests.uint32-pref undefined 1
javascript.options.use_emulates_undefined_fuse undefined true
javascript.options.wasm_exnref undefined false
layout.css.more_color_4.enabled true undefined
layout.css.overflow-overlay.enabled true undefined
layout.cursor.block.enabled true undefined
layout.tables.scrollable-cells undefined false
layout.use-plugin-fallback false undefined
media.allow-audio-non-utility true false
media.getusermedia.microphone.prefer_voice_stream_with_processing.enabled undefined true
memory.phc.avg_delay.first undefined 65536
memory.phc.avg_delay.normal undefined 16384
memory.phc.avg_delay.page_reuse undefined 262144
network.cache.purgebyfrecency_minprogress_disk undefined 0
network.cache.purgebyfrecency_minprogress_memory undefined 0
network.dns.native_https_query_in_automation undefined false
network.http.http2.move_to_pending_list_after_network_change false true
network.http_index_format.allowed_schemes undefined file,moz-gio
pdfjs.enableML undefined false
plugin.default.state 1 undefined
privacy.sanitize.sanitizeOnShutdown.hasMigratedToNewPrefs undefined false
privacy.webrtc.showIndicatorsOnMacos14AndAbove undefined true
toolkit.telemetry.enabled false true
ui.mouse.right_click.move_caret.stop_if_in_focused_editable_node undefined false
widget.disable_file_pickers undefined false
widget.gtk.titlebar-action-middle-click-enabled undefined false