This is difference between the default preference of Firefox 75.0 beta 2 and one of 74.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 74.0Firefox 75.0 beta 2
app.normandy.onsync_skew_sec 3300 600
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/firefox/ https://www.mozilla.org/firefox/beta
browser.aboutwelcome.enabled undefined false
browser.aboutwelcome.log undefined warn
browser.cache.disk.content_type_media_limit undefined 50
browser.cache.offline.storage.enable true false
browser.contentblocking.control-center.ui.showAllowedLabels false undefined
browser.contentblocking.control-center.ui.showBlockedLabels true undefined
browser.contentblocking.report.lockwise.mobile-android.url undefined https://play.google.com/store/apps/details?id=mozilla.lockbox&referrer=utm_source%3Dprotection_report%26utm_content%3Dmobile_promotion
browser.contentblocking.report.lockwise.mobile-ios.url undefined https://apps.apple.com/app/id1314000270
browser.contentblocking.report.lockwise.url https://lockwise.firefox.com/?utm_source=firefox-desktop&utm_medium=referral&utm_campaign=about-protections&utm_content=about-protections undefined
browser.contentblocking.report.mobile-android.url undefined https://play.google.com/store/apps/details?id=org.mozilla.firefox&referrer=utm_source%3Dprotection_report%26utm_content%3Dmobile_promotion
browser.contentblocking.report.mobile-ios.url undefined https://apps.apple.com/app/firefox-private-safe-browser/id989804926
browser.contentblocking.report.show_mobile_app undefined false
browser.display.suppress_canvas_background_image_on_forced_colors undefined true
browser.newtabpage.activity-stream.discoverystream.isCollectionDismissible undefined false
browser.newtabpage.activity-stream.discoverystream.lang-layout-config en undefined
browser.newtabpage.activity-stream.discoverystream.region-basic-layout undefined true
browser.newtabpage.activity-stream.discoverystream.region-layout-config undefined US,CA
browser.newtabpage.activity-stream.discoverystream.region-spocs-config undefined US
browser.newtabpage.activity-stream.discoverystream.region-stories-config undefined US,DE,CA
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.privatebrowsing.forceMediaMemoryCache undefined false
browser.search.geoip.timeout 3000 undefined
browser.search.geoip.url https://location.services.mozilla.com/v1/country?key=%MOZILLA_API_KEY% undefined
browser.startup.homepage.abouthome_cache.enabled undefined false
browser.tabs.remote.separatePrivilegedMozillaWebContentProcess false true
browser.urlbar.clickSelectsAll false undefined
browser.urlbar.doubleClickSelectsAll true undefined
browser.urlbar.openViewOnFocus false true
browser.urlbar.update1 false true
browser.urlbar.update1.interventions false true
browser.urlbar.update1.searchTips false true
browser.urlbar.update1.view.stripHttps false true
devtools.debugger.features.async-captured-stacks undefined false
devtools.debugger.features.async-live-stacks false true
devtools.debugger.features.command-click undefined false
devtools.inspector.showUserAgentShadowRoots false undefined
devtools.netmonitor.columnsData [{"name":"status","minWidth":30,"width":5}, {"name":"method","minWidth":30,"width":5}, {"name":"domain","minWidth":30,"width":10}, {"name":"file","minWidth":30,"width":25}, {"name":"url","minWidth":30,"width":25}, {"name":"cause","minWidth":30,"width":10},{"name":"type","minWidth":30,"width":5},{"name":"transferred","minWidth":30,"width":10},{"name":"contentSize","minWidth":30,"width":5},{"name":"waterfall","minWidth":150,"width":25}] [{"name":"status","minWidth":30,"width":5}, {"name":"method","minWidth":30,"width":5}, {"name":"domain","minWidth":30,"width":10}, {"name":"file","minWidth":30,"width":25}, {"name":"url","minWidth":30,"width":25}, {"name":"cause","minWidth":30,"width":10},{"name":"initiator","minWidth":30,"width":10},{"name":"type","minWidth":30,"width":5},{"name":"transferred","minWidth":30,"width":10},{"name":"contentSize","minWidth":30,"width":5},{"name":"waterfall","minWidth":150,"width":15}]
devtools.netmonitor.visibleColumns ["status","method","domain","file","cause","type","transferred","contentSize","waterfall"] ["status","method","domain","file","cause","initiator","type","transferred","contentSize","waterfall"]
devtools.performance.popup.intro-displayed undefined false
devtools.recordreplay.allowRepaintFailures true undefined
devtools.recordreplay.cloudServer undefined
devtools.recordreplay.enabled false undefined
devtools.recordreplay.fastLogpoints false undefined
devtools.recordreplay.includeSystemScripts false undefined
devtools.recordreplay.logging false undefined
devtools.recordreplay.loggingFull false undefined
devtools.recordreplay.mvp.enabled false undefined
devtools.webconsole.input.context undefined false
dom.IntersectionObserverExplicitDocumentRoot.enabled undefined false
dom.animations-api.autoremove.enabled false true
dom.animations-api.getAnimations.enabled false true
dom.animations-api.implicit-keyframes.enabled false true
dom.animations-api.timelines.enabled false true
dom.confirm_repost.testing.always_accept undefined false
dom.css_pseudo_element.enabled undefined false
dom.document.exec_command.nested_calls_allowed undefined false
dom.forms.requestsubmit.enabled false true
dom.image-lazy-loading.enabled false true
dom.image-lazy-loading.root-margin.bottom undefined 0.0
dom.image-lazy-loading.root-margin.bottom.percentage undefined false
dom.image-lazy-loading.root-margin.left undefined 0.0
dom.image-lazy-loading.root-margin.left.percentage undefined false
dom.image-lazy-loading.root-margin.right undefined 0.0
dom.image-lazy-loading.root-margin.right.percentage undefined false
dom.image-lazy-loading.root-margin.top undefined 0.0
dom.image-lazy-loading.root-margin.top.percentage undefined false
dom.ipc.forkserver.enable undefined false
dom.reporting.crash.enabled undefined false
dom.storage.next_gen false true
dom.targetBlankNoOpener.enabled false true
dom.vr.openvr.action_input true undefined
extensions.webcompat-reporter.enabled false true
geo.provider-country.network.scan undefined false
geo.provider-country.network.url undefined https://location.services.mozilla.com/v1/country?key=%MOZILLA_API_KEY%
geo.provider.network.timeToWaitBeforeSending undefined 5000
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.batching.lookback undefined 10
gfx.webrender.debug.disable-raster-root-scale undefined false
gfx.webrender.dl.dump-content-serialized undefined false
javascript.options.shared_memory false true
layout.css.comparison-functions.enabled false true
layout.css.conic-gradient.enabled undefined false
layout.css.focus-visible.enabled undefined false
layout.css.moz-document.url-prefix-hack.enabled true false
layout.css.serialize-grid-implicit-tracks true false
layout.css.webkit-appearance.enabled true undefined
layout.dynamic-reflow-roots.enabled false true
media.eme.require-app-approval undefined false
media.mediacontrol.eligible.media.duration.s undefined 3.0
media.mediacontrol.stopcontrol.timer.ms undefined 60000
media.mediasource.vp9.enabled undefined true
media.mediasource.webm.enabled false true
media.peerconnection.dtls.version.min 770 771
mousebutton.4th.enabled undefined true
mousebutton.5th.enabled undefined true
network.cookie.sameSite.laxPlusPOST.timeout undefined 120
network.cookieJarSettings.unblocked_for_testing undefined false
network.cookieSettings.unblocked_for_testing false undefined
network.trr.fetch_off_main_thread undefined true
pdfjs.ignoreDestinationZoom undefined false
permissions.isolateBy.privateBrowsing false true
print.use_global_printsettings true undefined
privacy.annotate_channels.strict_list.enabled false true
privacy.purge_trackers.enabled undefined false
privacy.purge_trackers.logging.enabled undefined false
privacy.purge_trackers.max_purge_count undefined 100
remote.log.truncate undefined true
security.allow_parent_unrestricted_js_loads false true
security.block_Worker_with_wrong_mime false true
security.disallow_non_local_systemprincipal_in_tests undefined false
security.remote_settings.crlite_filters.enabled false true
security.remote_settings.intermediates.enabled false true
security.strict_security_checks.enabled false undefined
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.passwords.validation.enabled undefined true
signon.passwordEditCapture.enabled undefined false
toolkit.shutdown.lateWriteChecksStage 0 1
toolkit.telemetry.enabled false true
toolkit.telemetry.geckoview.maxBatchStalenessMS undefined 60000
view_source.tab_size undefined 4
webgl.default-low-power true undefined
webgl.power-preference-override undefined 0
widget.disable-native-theme false undefined
widget.disable-native-theme-for-content undefined false
widget.wayland-cache-mode undefined 0
widget.wayland-dmabuf-basic-compositor.enabled undefined false
widget.wayland-dmabuf-textures.enabled undefined false
widget.wayland-dmabuf-vaapi.enabled undefined false
widget.wayland-dmabuf-webgl.enabled undefined false
widget.wayland.use-opaque-region undefined true