This is difference between the default preference of Firefox 40.0 beta 3 and one of 40.0.2.

Default pref Javascript files (Firefox 40.0.2 for Linux x86_64):
(omni.ja){/greprefs.js,/defaults/pref/services-sync.js}, (browser/omni.ja)/defaults/preferences/{firefox.js,firefox-branding.js,firefox-l10n.js}, (webapprt/omni.ja)/defaults/preferences/prefs.js
Default pref Javascript files (Firefox 41.0 beta 3 for Linux x86_64):
(omni.ja){/greprefs.js,/defaults/pref/services-sync.js}, (browser/omni.ja)/defaults/preferences/{firefox.js,firefox-branding.js,firefox-l10n.js}, (webapprt/omni.ja)/defaults/preferences/prefs.js
PrefFirefox 40.0.2Firefox 41.0 beta 3
app.update.badgeWaitTime3456000
browser.download.debugfalseundefined
browser.download.loglevelundefinedError
browser.newtab.urlabout:newtabundefined
browser.pocket.enabledLocalesen-US en-GB en-ZA de es-ES ja ja-JP-mac rucs de en-GB en-US en-ZA es-ES es-MX fr hu it ja ja-JP-mac ko nl pl pt-BR pt-PT ru zh-CN zh-TW
browser.safebrowsing.downloads.remote.timeout_msundefined10000
browser.safebrowsing.reportErrorURLhttp://%LOCALE%.phish-error.mozilla.com/?hl=%LOCALE%undefined
browser.safebrowsing.reportGenericURLhttp://%LOCALE%.phish-generic.mozilla.com/?hl=%LOCALE%undefined
browser.safebrowsing.reportMalwareErrorURLhttp://%LOCALE%.malware-error.mozilla.com/?hl=%LOCALE%undefined
browser.safebrowsing.reportMalwareMistakeURLundefinedhttps://%LOCALE%.malware-error.mozilla.com/?hl=%LOCALE%&url=
browser.safebrowsing.reportMalwareURLhttp://%LOCALE%.malware-report.mozilla.com/?hl=%LOCALE%undefined
browser.safebrowsing.reportPhishMistakeURLundefinedhttps://%LOCALE%.phish-error.mozilla.com/?hl=%LOCALE%&url=
browser.safebrowsing.reportPhishURLhttp://%LOCALE%.phish-report.mozilla.com/?hl=%LOCALE%https://%LOCALE%.phish-report.mozilla.com/?hl=%LOCALE%&url=
browser.safebrowsing.reportURLhttps://safebrowsing.google.com/safebrowsing/report?undefined
browser.search.geoSpecificDefaultstruefalse
browser.translation.engineundefinedbing
browser.urlbar.restrict.searchesundefined$
browser.urlbar.suggest.searchesundefinedfalse
canvas.capturestream.enabledundefinedfalse
caret.manages-android-actionbarundefinedfalse
datareporting.healthreport.about.reportUrlUnifiedundefinedhttps://fhr.cdn.mozilla.net/%LOCALE%/v4/
datareporting.healthreport.service.providerCategorieshealthreport-js-provider-defaulthealthreport-js-provider-default,healthreport-js-provider-beta
devtools.debugger.ui.panes-sources-width200undefined
devtools.debugger.ui.panes-workers-and-sources-widthundefined200
devtools.debugger.workersundefinedfalse
devtools.devedition.promo.enabledfalsetrue
devtools.inspector.animationInspectorV3undefinedfalse
devtools.inspector.show_pseudo_elementstruefalse
devtools.netmonitor.har.compressundefinedfalse
devtools.netmonitor.har.defaultFileNameundefinedArchive %y-%m-%d %H-%M-%S
devtools.netmonitor.har.defaultLogDirundefined
devtools.netmonitor.har.enableAutoExportToFileundefinedfalse
devtools.netmonitor.har.forceExportundefinedfalse
devtools.netmonitor.har.includeResponseBodiesundefinedtrue
devtools.netmonitor.har.jsonpundefinedfalse
devtools.netmonitor.har.jsonpCallbackundefined
devtools.netmonitor.har.pageLoadedTimeoutundefined1500
devtools.performance.ui.enable-allocationsundefinedfalse
devtools.performance.ui.enable-jit-optimizationsundefinedfalse
devtools.performance.ui.show-jit-optimizationsfalseundefined
devtools.toolbox.previousHostundefinedside
dom.caches.enabledfalsetrue
dom.messageChannel.enabledundefinedtrue
dom.push.http2.maxRetriesundefined2
dom.push.http2.reset_retry_count_after_msundefined60000
dom.push.http2.retryIntervalundefined5000
dom.url.getters_decode_hashundefinedfalse
dom.workers.websocket.enabledtrueundefined
font.default.thserifsans-serif
font.mathfont-familyLatin Modern Math, XITS Math, STIX Math, Cambria Math, Asana Math, TeX Gyre Bonum Math, TeX Gyre Pagella Math, TeX Gyre Termes Math, Neo Euler, Lucida Bright Math, MathJax_Main, STIXNonUnicode, STIXSizeOneSym, STIXGeneral, Standard Symbols L, DejaVu Sansundefined
font.minimum-size.x-mathundefined0
font.name-list.serif.x-mathundefinedLatin Modern Math, XITS Math, Cambria Math, TeX Gyre Bonum Math, TeX Gyre Pagella Math, TeX Gyre Schola, TeX Gyre Termes Math, STIX Math, Asana Math, STIXGeneral, DejaVu Serif, DejaVu Sans, serif
font.name.monospace.arundefinedmonospace
font.name.monospace.x-armnundefinedmonospace
font.name.monospace.x-bengundefinedmonospace
font.name.monospace.x-cansundefinedmonospace
font.name.monospace.x-devanagariundefinedmonospace
font.name.monospace.x-ethiundefinedmonospace
font.name.monospace.x-georundefinedmonospace
font.name.monospace.x-gujrundefinedmonospace
font.name.monospace.x-guruundefinedmonospace
font.name.monospace.x-khmrundefinedmonospace
font.name.monospace.x-kndaundefinedmonospace
font.name.monospace.x-mathundefinedmonospace
font.name.monospace.x-mlymundefinedmonospace
font.name.monospace.x-oryaundefinedmonospace
font.name.monospace.x-sinhundefinedmonospace
font.name.monospace.x-tamilundefinedmonospace
font.name.monospace.x-teluundefinedmonospace
font.name.monospace.x-tibtundefinedmonospace
font.name.monospace.zh-TWundefinedmonospace
font.name.sans-serif.arundefinedsans-serif
font.name.sans-serif.x-armnundefinedsans-serif
font.name.sans-serif.x-bengundefinedsans-serif
font.name.sans-serif.x-cansundefinedsans-serif
font.name.sans-serif.x-devanagariundefinedsans-serif
font.name.sans-serif.x-ethiundefinedsans-serif
font.name.sans-serif.x-georundefinedsans-serif
font.name.sans-serif.x-gujrundefinedsans-serif
font.name.sans-serif.x-guruundefinedsans-serif
font.name.sans-serif.x-khmrundefinedsans-serif
font.name.sans-serif.x-kndaundefinedsans-serif
font.name.sans-serif.x-mathundefinedsans-serif
font.name.sans-serif.x-mlymundefinedsans-serif
font.name.sans-serif.x-oryaundefinedsans-serif
font.name.sans-serif.x-sinhundefinedsans-serif
font.name.sans-serif.x-tamilundefinedsans-serif
font.name.sans-serif.x-teluundefinedsans-serif
font.name.sans-serif.x-tibtundefinedsans-serif
font.name.sans-serif.zh-TWundefinedsans-serif
font.name.serif.arundefinedserif
font.name.serif.x-armnundefinedserif
font.name.serif.x-bengundefinedserif
font.name.serif.x-cansundefinedserif
font.name.serif.x-devanagariundefinedserif
font.name.serif.x-ethiundefinedserif
font.name.serif.x-georundefinedserif
font.name.serif.x-gujrundefinedserif
font.name.serif.x-guruundefinedserif
font.name.serif.x-khmrundefinedserif
font.name.serif.x-kndaundefinedserif
font.name.serif.x-mathundefinedLatin Modern Math
font.name.serif.x-mlymundefinedserif
font.name.serif.x-oryaundefinedserif
font.name.serif.x-sinhundefinedserif
font.name.serif.x-tamilundefinedserif
font.name.serif.x-teluundefinedserif
font.name.serif.x-tibtundefinedserif
font.name.serif.zh-TWundefinedserif
full-screen-api.content-onlyfalseundefined
general.useragent.localeen-USeo
gfx.font_rendering.fontconfig.fontlist.enabledundefinedfalse
identity.fxaccounts.profile_image.enabledundefinedtrue
intl.ime.hack.on_ime_unaware_apps.fire_key_events_for_compositionundefinedfalse
javascript.options.compact_on_user_inactive_delayundefined300000
layers.compositor-lru-sizeundefined0
layers.deaa.enabledundefinedtrue
layers.offmainthreadcomposition.async-animationsfalsetrue
layout.accessiblecaret.bar.widthundefined2.0
layout.accessiblecaret.enabledundefinedfalse
layout.accessiblecaret.heightundefined47.0
layout.accessiblecaret.margin-leftundefined-23.5
layout.accessiblecaret.timeout_msundefined3000
layout.accessiblecaret.widthundefined44.0
layout.css.contain.enabledundefinedfalse
layout.css.font-loading-api.enabledfalsetrue
layout.css.text-combine-upright.enabledundefinedfalse
layout.css.vertical-text.enabledfalsetrue
loop.textChat.enabledundefinedtrue
media.format-reader.mp4undefinedtrue
media.mediasource.format-readerundefinedfalse
media.mediasource.format-reader.mp4undefinedtrue
media.peerconnection.default_iceservers[{"urls": ["stun:stun.services.mozilla.com"]}][]
media.peerconnection.ice.relay_onlyundefinedfalse
media.peerconnection.ice.stun_client_maximum_transmitsundefined7
media.peerconnection.ice.tcpundefinedfalse
media.peerconnection.ice.trickle_grace_periodundefined5000
network.dns.get-ttlfalsetrue
network.http.enable-packaged-appsundefinedfalse
network.http.spdy.enabled.http2drafttrueundefined
network.manage-offline-statusfalsetrue
plugins.enumerable_names*undefined
print.postscript.orientationportraitundefined
print.postscript.paper_sizeletterundefined
print.postscript.print_commandlpr ${MOZ_PRINTER_NAME:+-P"$MOZ_PRINTER_NAME"}undefined
print.print_commandlpr ${MOZ_PRINTER_NAME:+-P"$MOZ_PRINTER_NAME"}undefined
selectioncaret.observes.compositionsundefinedfalse
selectioncaret.visibility.affectscaretundefinedfalse
services.sync.log.appender.consoleWarnFatal
signon.rememberSignons.visibilityTogglefalsetrue
signon.ui.experimentalundefinedfalse
svg.transform-origin.enabledundefinedfalse
toolkit.asyncshutdown.logundefinedfalse
toolkit.telemetry.unifiedIsOptIntrueundefined
touchcaret.extendedvisibilityundefinedfalse
view_source.tabundefinedtrue
webgl.disable-debug-renderer-infoundefinedfalse
webgl.disable-fail-if-major-performance-caveatundefinedfalse
webgl.renderer-string-overrideundefined
webgl.vendor-string-overrideundefined
xpinstall.signatures.requiredfalsetrue