This is difference between the default preference of Firefox 17.0 beta1 and one of 16.0.1.

Default pref Javascript files (Firefox 16.0.1 for linux):
(omni.ja){/greprefs.js,/defaults/preferences/{firefox.js,firefox-branding.js,firefox-l10n.js,services-sync.js,services-aitc.js}}
Default pref Javascript files (Firefox 17.0 beta1 for linux):
(omni.ja){/greprefs.js,/defaults/preferences/{firefox.js,firefox-branding.js,firefox-l10n.js,services-sync.js,services-aitc.js}}
PrefFirefox 16.0.1Firefox 17.0 beta 1
alerts.slideIncrement1undefined
alerts.slideIncrementTime10undefined
alerts.totalOpenTime4000undefined
browser.cache.disk.smart_size.use_old_maxundefinedtrue
browser.newtab.preloadundefinedfalse
browser.newtabpage.columnsundefined3
browser.newtabpage.rowsundefined3
browser.safebrowsing.dataProvider0undefined
browser.safebrowsing.debugundefinedfalse
browser.safebrowsing.gethashURLundefinedhttp://safebrowsing.clients.google.com/safebrowsing/gethash?client=SAFEBROWSING_ID&appver=%VERSION%&pver=2.2
browser.safebrowsing.keyURLundefinedhttps://sb-ssl.google.com/safebrowsing/newkey?client=SAFEBROWSING_ID&appver=%VERSION%&pver=2.2
browser.safebrowsing.provider.0.gethashURLhttp://safebrowsing.clients.google.com/safebrowsing/gethash?client={moz:client}&appver={moz:version}&pver=2.2undefined
browser.safebrowsing.provider.0.keyURLhttps://sb-ssl.google.com/safebrowsing/newkey?client={moz:client}&appver={moz:version}&pver=2.2undefined
browser.safebrowsing.provider.0.nameGoogleundefined
browser.safebrowsing.provider.0.reportErrorURLhttp://{moz:locale}.phish-error.mozilla.com/?hl={moz:locale}undefined
browser.safebrowsing.provider.0.reportGenericURLhttp://{moz:locale}.phish-generic.mozilla.com/?hl={moz:locale}undefined
browser.safebrowsing.provider.0.reportMalwareErrorURLhttp://{moz:locale}.malware-error.mozilla.com/?hl={moz:locale}undefined
browser.safebrowsing.provider.0.reportMalwareURLhttp://{moz:locale}.malware-report.mozilla.com/?hl={moz:locale}undefined
browser.safebrowsing.provider.0.reportPhishURLhttp://{moz:locale}.phish-report.mozilla.com/?hl={moz:locale}undefined
browser.safebrowsing.provider.0.reportURLhttp://safebrowsing.clients.google.com/safebrowsing/report?undefined
browser.safebrowsing.provider.0.updateURLhttp://safebrowsing.clients.google.com/safebrowsing/downloads?client={moz:client}&appver={moz:version}&pver=2.2undefined
browser.safebrowsing.reportErrorURLundefinedhttp://%LOCALE%.phish-error.mozilla.com/?hl=%LOCALE%
browser.safebrowsing.reportGenericURLundefinedhttp://%LOCALE%.phish-generic.mozilla.com/?hl=%LOCALE%
browser.safebrowsing.reportMalwareErrorURLundefinedhttp://%LOCALE%.malware-error.mozilla.com/?hl=%LOCALE%
browser.safebrowsing.reportMalwareURLundefinedhttp://%LOCALE%.malware-report.mozilla.com/?hl=%LOCALE%
browser.safebrowsing.reportPhishURLundefinedhttp://%LOCALE%.phish-report.mozilla.com/?hl=%LOCALE%
browser.safebrowsing.reportURLundefinedhttp://safebrowsing.clients.google.com/safebrowsing/report?
browser.safebrowsing.updateURLundefinedhttp://safebrowsing.clients.google.com/safebrowsing/downloads?client=SAFEBROWSING_ID&appver=%VERSION%&pver=2.2
device.motion.enabledtrueundefined
device.sensors.enabledundefinedtrue
devtools.debugger.ui.stackframes-pane-visibleundefinedtrue
devtools.debugger.ui.variables-pane-visibleundefinedtrue
devtools.inspector.highlighterShowInfobartrueundefined
devtools.inspector.highlighterShowVeiltrueundefined
devtools.webconsole.fontSizeundefined0
dom.idle-observers-api.fuzz_time.disabledundefinedtrue
dom.ipc.plugins.enabled.602plugin.sofalseundefined
dom.ipc.plugins.enabled.libvlcplugin.sofalseundefined
dom.ipc.plugins.enabled.nppdf.sofalseundefined
dom.mozContacts.whitelistundefined
dom.sms.whitelistundefined
font.size.inflation.mappingInterceptundefined1
general.useragent.override.aol.comundefinedGecko/[^ ]*#Gecko/20100101
general.useragent.site_specific_overridesundefinedtrue
gfx.canvas.azure.backendsundefinedcairo
gfx.canvas.azure.enabledundefinedfalse
image.mem.max_bytes_for_sync_decode150000undefined
javascript.options.mem.analysis_purge_mbundefined100
javascript.options.xml.contenttruefalse
layers.offmainthreadcomposition.animate-opacityundefinedfalse
layers.offmainthreadcomposition.animate-transformundefinedfalse
layers.offmainthreadcomposition.log-animationsundefinedfalse
layout.css.supports-rule.enabledundefinedfalse
media.navigator.enabledundefinedfalse
media.raw.enabledundefinedtrue
mousewheel.default.actionundefined1
mousewheel.default.delta_multiplier_xundefined100
mousewheel.default.delta_multiplier_yundefined100
mousewheel.default.delta_multiplier_zundefined100
mousewheel.horizscroll.withaltkey.action2undefined
mousewheel.horizscroll.withaltkey.numlines-1undefined
mousewheel.horizscroll.withaltkey.sysnumlinesfalseundefined
mousewheel.horizscroll.withcontrolkey.action0undefined
mousewheel.horizscroll.withcontrolkey.numlines1undefined
mousewheel.horizscroll.withcontrolkey.sysnumlinestrueundefined
mousewheel.horizscroll.withmetakey.action0undefined
mousewheel.horizscroll.withmetakey.numlines1undefined
mousewheel.horizscroll.withmetakey.sysnumlinestrueundefined
mousewheel.horizscroll.withnokey.action0undefined
mousewheel.horizscroll.withnokey.numlines1undefined
mousewheel.horizscroll.withnokey.sysnumlinestrueundefined
mousewheel.horizscroll.withshiftkey.action0undefined
mousewheel.horizscroll.withshiftkey.numlines1undefined
mousewheel.horizscroll.withshiftkey.sysnumlinestrueundefined
mousewheel.min_line_scroll_amountundefined5
mousewheel.with_alt.actionundefined1
mousewheel.with_alt.delta_multiplier_xundefined100
mousewheel.with_alt.delta_multiplier_yundefined100
mousewheel.with_alt.delta_multiplier_zundefined100
mousewheel.with_control.actionundefined3
mousewheel.with_control.delta_multiplier_xundefined100
mousewheel.with_control.delta_multiplier_yundefined100
mousewheel.with_control.delta_multiplier_zundefined100
mousewheel.with_meta.actionundefined1
mousewheel.with_meta.delta_multiplier_xundefined100
mousewheel.with_meta.delta_multiplier_yundefined100
mousewheel.with_meta.delta_multiplier_zundefined100
mousewheel.with_shift.actionundefined2
mousewheel.with_shift.delta_multiplier_xundefined100
mousewheel.with_shift.delta_multiplier_yundefined100
mousewheel.with_shift.delta_multiplier_zundefined100
mousewheel.with_win.actionundefined1
mousewheel.with_win.delta_multiplier_xundefined100
mousewheel.with_win.delta_multiplier_yundefined100
mousewheel.with_win.delta_multiplier_zundefined100
mousewheel.withaltkey.action0undefined
mousewheel.withaltkey.numlines1undefined
mousewheel.withaltkey.sysnumlinesfalseundefined
mousewheel.withcontrolkey.action3undefined
mousewheel.withcontrolkey.numlines1undefined
mousewheel.withcontrolkey.sysnumlinesfalseundefined
mousewheel.withmetakey.action0undefined
mousewheel.withmetakey.numlines1undefined
mousewheel.withmetakey.sysnumlinestrueundefined
mousewheel.withnokey.action0undefined
mousewheel.withnokey.numlines6undefined
mousewheel.withnokey.sysnumlinestrueundefined
mousewheel.withshiftkey.action2undefined
mousewheel.withshiftkey.numlines1undefined
mousewheel.withshiftkey.sysnumlinesfalseundefined
network.http.keep-alivetrueundefined
network.http.max-connections-per-server15undefined
network.http.proxy.keep-alivetrueundefined
network.http.spdy.send-buffer-sizeundefined131072
nglayout.debug.widget_update_flashingundefinedfalse
services.sync.log.logger.addonutilsundefinedDebug
social.activation.whitelistundefinedhttps://motown-dev.mozillalabs.com
social.activeundefinedfalse
social.manifest.motown{"origin":"https://motown-dev.mozillalabs.com","name":"MoTown","workerURL":"https://motown-dev.mozillalabs.com/social/worker.js","iconURL":"https://motown-dev.mozillalabs.com/images/motown-icon.png"}{"origin":"https://motown-dev.mozillalabs.com","name":"MoTown","workerURL":"https://motown-dev.mozillalabs.com/social/worker.js","iconURL":"https://motown-dev.mozillalabs.com/images/motown-icon.png","sidebarURL":"https://motown-dev.mozillalabs.com/social/sidebar"}
social.sidebar.openundefinedtrue
social.toast-notifications.enabledundefinedtrue
startup.homepage_override_urlhttp://www.mozilla.com/%LOCALE%/%APP%/%VERSION%/whatsnew/?oldversion=%OLD_VERSION%
svg.display-lists.hit-testing.enabledundefinedtrue
svg.display-lists.painting.enabledundefinedtrue
urlclassifier.lookupcachemax1048576undefined
urlclassifier.randomizeclientundefinedtrue
urlclassifier.updatecachemax41943040undefined
webgl.default-no-alphaundefinedfalse
webgl.force-layers-readbackundefinedfalse
webgl.prefer-16bppundefinedfalse