This is difference between the default preference of Firefox 65.0.1 beta 4 and one of 62.0.

Preference difference
PrefFirefox 65.0.1Firefox 66.0 beta 9
app.normandy.remotesettings.enabledundefinedfalse
app.update.download.backgroundInterval0undefined
app.update.url.detailshttps://www.mozilla.org/%LOCALE%/firefox/noteshttps://www.mozilla.org/%LOCALE%/firefox/beta/notes
app.update.url.manualhttps://www.mozilla.org/firefox/https://www.mozilla.org/firefox/beta
apz.allow_checkerboardingtrueundefined
breakpad.reportURLhttps://crash-stats.mozilla.com/report/index/https://crash-stats.mozilla.org/report/index/
browser.chrome.errorReporter.enabledfalseundefined
browser.chrome.errorReporter.logLevelErrorundefined
browser.chrome.errorReporter.projectId339undefined
browser.chrome.errorReporter.publicKeyc709cb7a2c0b4f0882fcc84a5af161ecundefined
browser.chrome.errorReporter.sampleRate0.001undefined
browser.chrome.errorReporter.submitUrlhttps://sentry.prod.mozaws.net/api/339/store/undefined
browser.newtabpage.activity-stream.improvesearch.handoffToAwesomebarundefinedfalse
browser.newtabpage.activity-stream.improvesearch.topSiteSearchShortcutsfalsetrue
browser.privatebrowsing.searchUIundefinedfalse
browser.safebrowsing.passwords.enabledfalseundefined
browser.safebrowsing.provider.mozilla.listsbase-track-digest256,mozstd-trackwhite-digest256,content-track-digest256,mozplugin-block-digest256,mozplugin2-block-digest256,block-flash-digest256,except-flash-digest256,allow-flashallow-digest256,except-flashallow-digest256,block-flashsubdoc-digest256,except-flashsubdoc-digest256,except-flashinfobar-digest256,ads-track-digest256,social-track-digest256,analytics-track-digest256base-track-digest256,mozstd-trackwhite-digest256,content-track-digest256,mozplugin-block-digest256,mozplugin2-block-digest256,block-flash-digest256,except-flash-digest256,allow-flashallow-digest256,except-flashallow-digest256,block-flashsubdoc-digest256,except-flashsubdoc-digest256,ads-track-digest256,social-track-digest256,analytics-track-digest256,base-fingerprinting-track-digest256,content-fingerprinting-track-digest256,base-cryptomining-track-digest256,content-cryptomining-track-digest256,fanboyannoyance-ads-digest256,fanboysocial-ads-digest256,easylist-ads-digest256,easyprivacy-ads-digest256,adguard-ads-digest256
browser.sanitizer.loglevelundefinedWarn
browser.security.newcerterrorpage.mitm.enabledfalsetrue
browser.tabs.drawInTitlebarfalseundefined
devtools.debugger.event-listener-breakpointsundefined[]
devtools.debugger.event-listeners-visibleundefinedfalse
devtools.debugger.features.event-listeners-breakpointsundefinedfalse
devtools.debugger.features.log-pointsundefinedfalse
devtools.debugger.features.origial-blackboxfalseundefined
devtools.debugger.features.original-blackboxundefinedtrue
devtools.debugger.features.windowless-workersundefinedfalse
devtools.inspector.flexboxHighlighter.combineundefinedfalse
devtools.inspector.new-rulesview.enabledundefinedfalse
devtools.inspector.scrollable-badges.enabledundefinedfalse
devtools.webconsole.input.editorundefinedfalse
devtools.webconsole.jsterm.reverse-searchtrueundefined
dom.inputevent.inputtype.enabledundefinedtrue
dom.ipc.processCount48
dom.ipc.scheduler.chaoticSchedulingfalseundefined
dom.ipc.scheduler.preemptionfalseundefined
dom.ipc.scheduler.threadCount2undefined
dom.ipc.scheduler.useMultipleQueuestrueundefined
dom.media.autoplay.autoplay-policy-apiundefinedfalse
dom.vr.openvr.action_inputundefinedfalse
dom.window.event.enabledfalsetrue
extensions.pocket.apiundefinedapi.getpocket.com
extensions.pocket.siteundefinedgetpocket.com
extensions.webcompat-reporter.enabledfalsetrue
extensions.webextensions.ExtensionStorageIDB.enabledfalsetrue
gfx.webrender.allundefinedfalse
gfx.webrender.debug.gpu-cacheundefinedfalse
gfx.webrender.debug.picture-cachingundefinedfalse
gfx.webrender.debug.primitivesundefinedfalse
gfx.webrender.debug.texture-cache.disable-shrinkundefinedfalse
gfx.webrender.enabledundefinedfalse
gfx.webrender.picture-cachingfalsetrue
intl.charset.fallback.utf8_for_filefalseundefined
javascript.options.dynamicImportundefinedfalse
javascript.options.wasm_verboseundefinedfalse
layout.css.background-blend-mode.enabledtrueundefined
layout.css.box-decoration-break.enabledtrueundefined
layout.css.color-adjust.enabledtrueundefined
layout.css.image-orientation.enabledtrueundefined
layout.css.isolation.enabledtrueundefined
layout.css.mix-blend-mode.enabledtrueundefined
layout.css.scroll-behavior.property-enabledtrueundefined
media.autoplay.ask-permissionfalseundefined
media.autoplay.default01
media.autoplay.enabled.user-gestures-neededfalsetrue
media.navigator.mediadatadecoder_h264_enabledfalsetrue
network.allow-experimentstrueundefined
network.http.accept.defaulttext/html,application/xhtml+xml,application/xml;q=0.9,image/webp,*/*;q=0.8undefined
network.http.send_window_size01024
network.process.enabledundefinedfalse
performance.adjust_to_machineundefinedfalse
performance.low_end_machineundefinedfalse
plugins.http_https_onlytrueundefined
privacy.trackingprotection.annotate_channelstrueundefined
privacy.trackingprotection.lower_network_priorityfalseundefined
security.certerrors.permanentOverrideundefinedtrue
security.remote_settings.intermediates.bucketundefinedsecurity-state
security.remote_settings.intermediates.checkedundefined0
security.remote_settings.intermediates.collectionundefinedintermediates
security.remote_settings.intermediates.enabledundefinedfalse
security.remote_settings.intermediates.signerundefinedonecrl.content-signature.mozilla.org
services.sync.prefs.sync.browser.contentblocking.categoryundefinedtrue
services.sync.prefs.sync.browser.contentblocking.introCountundefinedtrue
services.sync.prefs.sync.browser.crashReports.unsubmittedCheck.autoSubmit2undefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.feeds.section.highlightsundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.feeds.section.topstoriesundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.feeds.snippetsundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.feeds.topsitesundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.section.highlights.includeBookmarksundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.section.highlights.includeDownloadsundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.section.highlights.includePocketundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.section.highlights.includeVisitedundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.section.highlights.rowsundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.section.topstories.rowsundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.showSearchundefinedtrue
services.sync.prefs.sync.browser.newtabpage.activity-stream.topSitesRowsundefinedtrue
services.sync.prefs.sync.browser.taskbar.previews.enableundefinedtrue
services.sync.prefs.sync.media.eme.enabledundefinedtrue
urlclassifier.disallow_completionstest-malware-simple,test-harmful-simple,test-phish-simple,test-unwanted-simple,test-track-simple,test-trackwhite-simple,test-block-simple,goog-downloadwhite-digest256,base-track-digest256,mozstd-trackwhite-digest256,content-track-digest256,mozplugin-block-digest256,mozplugin2-block-digest256,block-flash-digest256,except-flash-digest256,allow-flashallow-digest256,except-flashallow-digest256,block-flashsubdoc-digest256,except-flashsubdoc-digest256,except-flashinfobar-digest256,goog-passwordwhite-proto,ads-track-digest256,social-track-digest256,analytics-track-digest256test-malware-simple,test-harmful-simple,test-phish-simple,test-unwanted-simple,test-track-simple,test-trackwhite-simple,test-block-simple,goog-downloadwhite-digest256,base-track-digest256,mozstd-trackwhite-digest256,content-track-digest256,mozplugin-block-digest256,mozplugin2-block-digest256,block-flash-digest256,except-flash-digest256,allow-flashallow-digest256,except-flashallow-digest256,block-flashsubdoc-digest256,except-flashsubdoc-digest256,goog-passwordwhite-proto,ads-track-digest256,social-track-digest256,analytics-track-digest256,base-fingerprinting-track-digest256,content-fingerprinting-track-digest256,base-cryptomining-track-digest256,content-cryptomining-track-digest256,fanboyannoyance-ads-digest256,fanboysocial-ads-digest256,easylist-ads-digest256,easyprivacy-ads-digest256,adguard-ads-digest256
urlclassifier.features.cryptomining.blacklistTablesundefinedbase-cryptomining-track-digest256
urlclassifier.features.cryptomining.whitelistTablesundefinedmozstd-trackwhite-digest256
urlclassifier.features.fingerprinting.blacklistTablesundefinedbase-fingerprinting-track-digest256
urlclassifier.features.fingerprinting.whitelistTablesundefinedmozstd-trackwhite-digest256
urlclassifier.flashInfobarTableexcept-flashinfobar-digest256undefined
widget.default-hidden-titlebarundefinedtrue
Default pref Javascript files
PrefFirefox 65.0.1Firefox 66.0 beta 9
browser/omni.ja.d/defaults/preferences/debugger.jspresentpresent
browser/omni.ja.d/defaults/preferences/devtools-client.jspresentpresent
browser/omni.ja.d/defaults/preferences/devtools-startup.jspresentpresent
browser/omni.ja.d/defaults/preferences/firefox-branding.jspresentpresent
browser/omni.ja.d/defaults/preferences/firefox-l10n.jspresentpresent
browser/omni.ja.d/defaults/preferences/firefox.jspresentpresent
browser/omni.ja.d/defaults/preferences/webide.jspresentpresent
omni.ja.d/defaults/pref/marionette.jspresentpresent
omni.ja.d/defaults/pref/services-sync.jspresentpresent
omni.ja.d/greprefs.jspresentpresent