This is difference between the default preference of Firefox 37.0 beta 3 and one of 36.0.1.

Default pref Javascript files (Firefox 36.0.1 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 37.0 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 36.0.1Firefox 37.0 beta 3
browser.display.use_document_colorstrueundefined
browser.preferences.inContentfalsetrue
browser.search.highlightCount50
camera.control.autofocus_moving_callback.enabledtrueundefined
datareporting.healthreport.service.providerCategorieshealthreport-js-provider-defaulthealthreport-js-provider-default,healthreport-js-provider-beta
devtools.devedition.promo.enabledfalsetrue
devtools.devedition.promo.urlhttps://mozilla.org/firefox/developerhttps://www.mozilla.org/firefox/developer/?utm_source=firefox-dev-tools&utm_medium=firefox-browser&utm_content=betadoorhanger
devtools.gcli.jquerySrchttp://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.jshttps://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js
devtools.gcli.lodashSrchttp://cdnjs.cloudflare.com/ajax/libs/lodash.js/2.4.1/lodash.min.jshttps://cdnjs.cloudflare.com/ajax/libs/lodash.js/2.4.1/lodash.min.js
devtools.gcli.underscoreSrchttp://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.6.0/underscore-min.jshttps://cdnjs.cloudflare.com/ajax/libs/underscore.js/1.7.0/underscore-min.js
dom.workers.websocket.enabledfalsetrue
image.mem.decodeondrawtruefalse
image.mem.max_ms_before_yield5undefined
image.multithreaded_decoding.enabledtrueundefined
javascript.options.mem.gc_min_empty_chunk_count01
layout.css.display-contents.enabledfalsetrue
media.gmp-gmpopenh264.provider.enabledtrueundefined
media.gmp-manager.logfalseundefined
media.navigator.video.max_fr060
media.navigator.video.max_fs012288
network.http.altsvc.enabledfalsetrue
network.http.altsvc.oefalsetrue
network.negotiate-auth.allow-insecure-ntlm-v1falseundefined
network.negotiate-auth.allow-insecure-ntlm-v1-httpstrueundefined
network.ntlm.send-lm-responsefalseundefined
network.websocket.extensions.stream-deflatefalseundefined
profiler.enabledfalseundefined
profiler.entries100000undefined
profiler.interval10undefined
security.ssl.false_start.require-forward-secrecytrueundefined
security.ssl.false_start.require-npntruefalse
security.ssl3.dhe_dss_aes_128_shatrueundefined
security.ssl3.dhe_dss_aes_256_shafalseundefined
security.ssl3.dhe_rsa_camellia_128_shafalseundefined
security.ssl3.dhe_rsa_camellia_256_shafalseundefined
security.ssl3.dhe_rsa_des_ede3_shafalseundefined
security.ssl3.ecdhe_rsa_des_ede3_shafalseundefined
security.ssl3.rsa_camellia_128_shafalseundefined
security.ssl3.rsa_camellia_256_shafalseundefined
security.tls.version.fallback-limit13
selectioncaret.noneditablefalseundefined
social.share.activationPanelEnabledfalsetrue
svg.marker-improvements.enabledfalsetrue