This is difference between the default preference of Firefox 9-beta and one of 8.

Default pref Javascript files:
(omni.jar){/greprefs.js,/defaults/pref/{firefox.js,firefox-branding.js,firefox-l10n.js,services-sync.js}}
PrefFirefox 8Firefox 9 beta 4
browser.download.saveLinkAsFilenameTimeout10004000
browser.overlink-delay7080
devtools.inspector.enabledtruefalse
devtools.styleinspector.enabledundefinedfalse
extensions.autoDisableScopes1015
geo.wifi.protocol0undefined
geo.wifi.urihttps://www.google.com/loc/jsonundefined
places.database.cache_to_memory_percentage6undefined
services.sync.errorhandler.networkFailureReportTimeoutundefined604800
services.sync.log.appender.file.maxErrorAgeundefined864000
services.sync.scheduler.activeInterval300600
services.sync.scheduler.immediateInterval6090
services.sync.scheduler.singleDeviceInterval360086400
startup.homepage_override_urlhttp://www.mozilla.com/%LOCALE%/%APP%/%VERSION%/whatsnew/
urlclassifier.lookupcachemaxundefined1048576
urlclassifier.updatecachemax10485760041943040