This is difference between the default preference of Firefox 24.0 beta 6 and one of 23.0.1.

Default pref Javascript files (Firefox 23.0.1 for Linux):
(omni.ja){/greprefs.js,/defaults/pref/services-sync.js}, (browser/omni.ja)defaults/preferences/{firefox.js,firefox-branding.js,firefox-l10n.js}
Default pref Javascript files (Firefox 24.0 beta 6 for Linux):
(omni.ja){/greprefs.js,/defaults/pref/services-sync.js}, (browser/omni.ja)defaults/preferences/{firefox.js,firefox-branding.js,firefox-l10n.js}
PrefFirefox 23.0.1Firefox 24.0 beta 6
app.releaseNotesURLhttp://www.mozilla.com/%LOCALE%/firefox/%VERSION%/releasenotes/undefined
app.support.baseURLhttp://support.mozilla.org/1/firefox/%VERSION%/%OS%/%LOCALE%/https://support.mozilla.org/1/firefox/%VERSION%/%OS%/%LOCALE%/
app.update.promptWaitTime86400172800
app.update.url.detailshttp://www.mozilla.com/%LOCALE%/firefox/releases/https://www.mozilla.org/%LOCALE%/firefox/notes
app.update.url.manualhttp://www.firefox.comhttps://www.mozilla.org/firefox/
app.vendorURLhttp://www.mozilla.com/%LOCALE%/firefox/undefined
browser.newtab.preloadfalsetrue
browser.safebrowsing.warning.infoURLhttp://www.mozilla.com/%LOCALE%/firefox/phishing-protection/https://www.mozilla.org/%LOCALE%/firefox/phishing-protection/
datareporting.healthreport.service.providerCategorieshealthreport-js-provider-defaulthealthreport-js-provider-default,healthreport-js-provider-beta
devtools.browserconsole.filter.csserrorundefinedtrue
devtools.browserconsole.filter.cssparserundefinedtrue
devtools.browserconsole.filter.errorundefinedtrue
devtools.browserconsole.filter.exceptionundefinedtrue
devtools.browserconsole.filter.infoundefinedtrue
devtools.browserconsole.filter.jslogundefinedtrue
devtools.browserconsole.filter.jswarnundefinedtrue
devtools.browserconsole.filter.logundefinedtrue
devtools.browserconsole.filter.networkundefinedtrue
devtools.browserconsole.filter.networkinfoundefinedtrue
devtools.browserconsole.filter.secerrorundefinedtrue
devtools.browserconsole.filter.secwarnundefinedtrue
devtools.browserconsole.filter.warnundefinedtrue
devtools.debugger.pause-on-exceptionsundefinedfalse
devtools.debugger.remote-autoconnectfalseundefined
devtools.debugger.remote-connection-retries3undefined
devtools.debugger.source-maps-enabledfalsetrue
devtools.debugger.ui.pause-on-exceptionsfalseundefined
devtools.debugger.ui.win-height400undefined
devtools.debugger.ui.win-width900undefined
devtools.debugger.ui.win-x0undefined
devtools.debugger.ui.win-y0undefined
devtools.telemetry.tools.opened.versionundefined{}
devtools.webconsole.filter.jslogundefinedtrue
devtools.webconsole.persistlogundefinedfalse
dom.forms.colorundefinedfalse
dom.future.enabledundefinedfalse
dom.gamepad.enabledundefinedfalse
dom.gamepad.non_standard_events.enabledundefinedfalse
dom.global-constructor.disable.mozContactundefinedtrue
dom.navigator-property.disable.mozContactsundefinedtrue
dom.navigator-property.disable.mozSettingsundefinedtrue
dom.popup_allowed_eventschange click dblclick mouseup reset submitchange click dblclick mouseup reset submit touchend
dom.w3c_touch_events.enabledundefined0
dom.workers.mem.gc_allocation_threshold_mb30undefined
extensions.blocklist.detailsURLhttps://www.mozilla.com/%LOCALE%/blocklist/https://www.mozilla.org/%LOCALE%/blocklist/
geo.wifi.uriundefinedhttps://www.googleapis.com/geolocation/v1/geolocate?key=%GOOGLE_API_KEY%
javascript.options.mem.gc_decommit_threshold_mbundefined32
javascript.options.methodjit.chromefalseundefined
javascript.options.methodjit.contentfalseundefined
javascript.options.methodjit_alwaysfalseundefined
layers.offmainthreadcomposition.animate-opacityfalseundefined
layers.offmainthreadcomposition.animate-transformfalseundefined
layers.offmainthreadcomposition.async-animationsundefinedfalse
layers.offmainthreadcomposition.log-animationsfalseundefined
layout.3d-transforms.enabledtrueundefined
layout.animated-image-layers.enabledundefinedfalse
layout.css.font-features.enabledundefinedfalse
layout.css.vertical-text.enabledundefinedfalse
layout.imagevisibility.enabledfalseundefined
media.gstreamer.enabledundefinedfalse
media.wakelock_timeoutundefined2000
media.webvtt.enabledundefinedfalse
network.http.bypass-cachelock-thresholdundefined200000
network.http.spdy.allow-pushundefinedtrue
network.http.spdy.push-allowanceundefined65536
network.http.spdy.use-alternate-protocoltrueundefined
plugin.expose_full_pathfalseundefined
plugin.persistentPermissionAlways.intervalInDaysundefined90
plugin.sessionPermissionNow.intervalInMinutesundefined60
services.sync.errorhandler.networkFailureReportTimeout6048001209600
services.sync.prefs.sync.security.OCSP.disable_button.managecrltrueundefined
startup.homepage_override_urlhttp://www.mozilla.com/%LOCALE%/firefox/%VERSION%/whatsnew/?oldversion=%OLD_VERSION%
startup.homepage_welcome_urlhttp://www.mozilla.com/%LOCALE%/firefox/%VERSION%/firstrun/https://www.mozilla.org/%LOCALE%/firefox/%VERSION%/firstrun/
webgl.enable-draft-extensionsundefinedfalse
webgl.max-warnings-per-contextundefined32