This is difference between the default preference of Firefox 30.0 beta 5 and one of 29.0.1.

Default pref Javascript files (Firefox 29.0.1 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 30.0 beta 5 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 29.0.1Firefox 30.0 beta 5
app.feedback.baseURLundefinedhttps://input.mozilla.org/%LOCALE%/feedback/%APP%/%VERSION%/
apz.printtreeundefinedfalse
browser.cache.auto_delete_cache_versionundefined1
browser.ctrlTab.recentlyUsedLimit7undefined
browser.safebrowsing.appRepURLundefinedhttps://sb-ssl.google.com/safebrowsing/clientreport/download?key=%GOOGLE_API_KEY%
browser.sessionstore.max_serialize_backundefined10
browser.sessionstore.max_serialize_forwardundefined-1
browser.tabs.remote.autostartundefinedfalse
canvas.hitregions.enabledundefinedfalse
datareporting.healthreport.service.providerCategorieshealthreport-js-provider-defaulthealthreport-js-provider-default,healthreport-js-provider-beta
devtools.command-button-paintflashing.enabledundefinedfalse
devtools.command-button-pick.enabledundefinedtrue
devtools.command-button-responsive.enabledundefinedtrue
devtools.command-button-scratchpad.enabledundefinedfalse
devtools.command-button-splitconsole.enabledundefinedtrue
devtools.command-button-tilt.enabledundefinedfalse
devtools.debugger.enable-content-actorstrueundefined
devtools.dump.emitundefinedfalse
devtools.gcli.allowSetfalseundefined
devtools.inspector.imagePreviewTooltipSizeundefined300
devtools.netmonitor.filtersundefined["all"]
devtools.webconsole.filter.networkinfotruefalse
dom.undo_manager.enabledundefinedfalse
dom.wakelock.enabledundefinedfalse
image.mozsamplesize.enabledundefinedfalse
intl.charset.fallback.tldundefinedtrue
javascript.options.baselinejitundefinedtrue
javascript.options.baselinejit.chrometrueundefined
javascript.options.baselinejit.contenttrueundefined
javascript.options.ionundefinedtrue
javascript.options.ion.chromefalseundefined
javascript.options.ion.contenttrueundefined
javascript.options.typeinferenceundefinedtrue
javascript.options.typeinference.chromefalseundefined
javascript.options.typeinference.contenttrueundefined
layers.enable-tilesundefinedfalse
layers.offmainthreadcomposition.log-animationsundefinedfalse
layers.use-deprecated-texturesfalsetrue
layout.css.background-blend-mode.enabledfalsetrue
layout.css.prefixes.box-sizingundefinedtrue
media.navigator.load_adapt.avg_secondsundefined3
media.navigator.load_adapt.high_loadundefined0.90
media.navigator.load_adapt.low_loadundefined0.40
media.navigator.load_adapt.measure_intervalundefined1000
media.peerconnection.identity.enabledundefinedfalse
media.peerconnection.identity.timeoutundefined5000
media.webaudio.enabledtrueundefined
memory.dump_reports_on_oomundefinedfalse
network.http.spdy.chunk-size409616000
network.http.tcp_keepalive.long_lived_connectionsundefinedtrue
network.http.tcp_keepalive.long_lived_idle_timeundefined600
network.http.tcp_keepalive.short_lived_connectionsundefinedtrue
network.http.tcp_keepalive.short_lived_idle_timeundefined10
network.http.tcp_keepalive.short_lived_timeundefined60
network.negotiate-auth.allow-insecure-ntlm-v1undefinedfalse
network.tcp.keepalive.enabledundefinedtrue
network.tcp.keepalive.idle_timeundefined600
network.tcp.keepalive.retry_intervalundefined1
plugin.default.state21
plugin.defaultXpi.stateundefined2
plugin.java.mimeundefinedapplication/x-java-vm
plugin.state.npatgpcundefined2
plugin.state.npbispbrowserundefined2
plugin.state.npesteid-firefox-pluginundefined2
plugins.hideMissingPluginsNotificationundefinedfalse
print.shrink-to-fit.scale-limit-percentundefined20
print.whileInPrintPreviewtrueundefined
signon.overrideAutocompletefalseundefined
signon.storeWhenAutocompleteOffundefinedtrue
social.enabledfalseundefined
social.sidebar.opentrueundefined
startup.homepage_override_urlhttps://www.mozilla.org/%LOCALE%/firefox/%VERSION%/whatsnew/?oldversion=%OLD_VERSION%
urlclassifier.disallow_completionsundefinedtest-malware-simple,test-phish-simple,goog-downloadwhite-digest256
urlclassifier.downloadAllowTableundefined
urlclassifier.downloadBlockTableundefinedgoog-badbinurl-shavar
urlclassifier.download_allow_tableundefined
urlclassifier.download_block_tableundefined
urlclassifier.malware_tablegoog-malware-shavargoog-malware-shavar,test-malware-simple
urlclassifier.phish_tablegoog-phish-shavargoog-phish-shavar,test-phish-simple
webgl.enable-privileged-extensionsundefinedfalse