This is difference between the default preference of Firefox 74.0 beta 3 and one of 73.0. This diff table is generated with my small script firefox-prefjs-surveyer.

Preference difference
PrefFirefox 73.0Firefox 74.0 beta 3
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
apz.touch_acceleration_factor_x undefined 1.0
apz.touch_acceleration_factor_y undefined 1.0
browser.cache.offline.storage.enable true false
browser.newtabpage.activity-stream.discoverystream.personalization.modelKeys undefined nb_model_business, nb_model_career, nb_model_education, nb_model_entertainment, nb_model_environment, nb_model_food, nb_model_gaming, nb_model_health_fitness, nb_model_parenting, nb_model_personal_finance, nb_model_politics, nb_model_science, nb_model_self_improvement, nb_model_sports, nb_model_technology, nb_model_travel
browser.newtabpage.activity-stream.discoverystream.personalization.version undefined 1
browser.newtabpage.activity-stream.feeds.recommendationproviderswitcher undefined true
browser.newtabpage.activity-stream.telemetry.ut.events false true
browser.tabs.allowTabDetach undefined true
browser.tabs.documentchannel false true
browser.tabs.remote.separatedMozillaDomains addons.cdn.mozilla.net,addons.mozilla.org,accounts.firefox.com addons.mozilla.org,accounts.firefox.com
browser.tabs.remote.useCORP false true
browser.urlbar.openViewOnFocus false true
browser.urlbar.update1 false true
browser.urlbar.update1.expandTextOnFocus false undefined
browser.urlbar.update1.interventions undefined true
browser.urlbar.update1.restrictTabAfterKeyboardFocus undefined true
browser.urlbar.update1.searchTips undefined true
browser.urlbar.update1.view.stripHttps false true
browser.urlbar.update2.expandTextOnFocus undefined false
canvas.mozgetasfile.enabled undefined false
corroborator.enabled false true
devtools.performance.recording.preset undefined web-developer
devtools.toolbox.content-frame true undefined
dom.about_newtab_sanitization.enabled undefined false
dom.image-lazy-loading.enabled undefined false
dom.input_events.beforeinput.enabled undefined false
dom.missing_prop_counters.enabled false true
dom.security.featurePolicy.enabled false true
dom.security.skip_about_page_csp_allowlist_and_assert undefined false
dom.security.skip_about_page_has_csp_assert undefined false
dom.security.skip_html_fragment_assertion undefined false
dom.security.skip_remote_script_assertion_in_system_priv_context undefined false
dom.serviceWorkers.parent_intercept false true
dom.storage.next_gen false true
dom.targetBlankNoOpener.enabled false true
dom.textMetrics.actualBoundingBox.enabled undefined true
dom.textMetrics.baselines.enabled undefined false
dom.textMetrics.emHeight.enabled undefined false
dom.textMetrics.fontBoundingBox.enabled undefined false
dom.worker.console.dispatch_events_to_main_thread undefined true
extensions.contentblocker.enabled false undefined
extensions.experiments.enabled undefined false
extensions.legacy.enabled false undefined
extensions.webcompat-reporter.enabled false true
full-screen-api.exit-on.windowOpen undefined true
full-screen-api.exit-on.windowRaise undefined true
geo.provider.network.timeout undefined 60000
geo.provider.network.url undefined https://location.services.mozilla.com/v1/geolocate?key=%MOZILLA_API_KEY%
geo.wifi.uri https://www.googleapis.com/geolocation/v1/geolocate?key=%GOOGLE_LOCATION_SERVICE_API_KEY% undefined
geo.wifi.xhr.timeout 60000 undefined
gfx.webrender.debug.tile-cache-logging undefined false
gfx.webrender.enable-item-cache undefined false
gfx.webrender.enable-low-priority-pool false true
gfx.webrender.enable-multithreading undefined true
javascript.options.parser_defer_allocation false undefined
javascript.options.property_error_message_fix undefined false
javascript.options.shared_memory false true
layout.css.comparison-functions.enabled undefined false
layout.css.moz-document.url-prefix-hack.enabled true false
layout.css.outline-style-auto.enabled false true
layout.css.parsing.parallel true undefined
layout.css.prefixes.columns undefined false
layout.css.serialize-grid-implicit-tracks undefined true
layout.css.text-underline-position.enabled false true
layout.css.use-counters-unimplemented.enabled false true
layout.css.use-counters.enabled false true
layout.dynamic-reflow-roots.enabled false true
media.audioipc.pool_size 1 undefined
media.audioipc.stack_size 262144 undefined
media.peerconnection.ice.obfuscate_host_addresses false true
media.videocontrols.picture-in-picture.keyboard-controls.enabled undefined false
network.socket.forcePort undefined
permissions.isolateBy.privateBrowsing false true
places.search.matchDiacritics undefined false
privacy.annotate_channels.strict_list.enabled false true
privacy.dynamic_firstparty.limitForeign undefined false
privacy.restrict3rdpartystorage.expiration_redirect undefined 900
privacy.restrict3rdpartystorage.heuristic.redirect undefined true
privacy.userContext.longPressBehavior 0 undefined
privacy.userContext.newTabContainerOnLeftClick.enabled undefined false
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.tls.version.min 1 3
services.sync.engine.bookmarks.validation.enabled undefined true
services.sync.engine.passwords.validation.enabled undefined true
signon.management.page.enabled true undefined
toolkit.shutdown.fastShutdownStage undefined 0
toolkit.shutdown.lateWriteChecksStage undefined 0
toolkit.telemetry.enabled false true
webgl.default-low-power false true
webgl.disable-extensions false undefined
webgl.out-of-process undefined false
widget.wayland_dmabuf_backend.enabled false undefined