This is difference between the default preference of Firefox 8.0-beta and one of 7.0.1.

Default pref Javascript files:
(omni.jar){/greprefs.js,/defaults/pref/{firefox.js,firefox-branding.js,firefox-l10n.js,services-sync.js}}
Firefox 7.0.1Firefox 8 beta 4
app.update.promptWaitTime4320086400
browser.sessionhistory.optimize_evictiontrueundefined
browser.sessionstore.max_concurrent_tabs3undefined
browser.sessionstore.restore_on_demandundefinedfalse
devtools.editor.componentundefinedtextarea
devtools.inspector.enabledfalsetrue
dom.workers.enabledundefinedtrue
dom.workers.maxPerDomainundefined20
extensions.autoDisableScopesundefined10
gfx.color_management.enablev4undefinedfalse
image.mem.decode_bytes_at_a_time2000004096
image.mem.max_ms_before_yield4005
intl.accept_charsetsiso-8859-1,*,utf-8undefined
intl.hyphenation-alias.af-*undefinedaf
intl.hyphenation-alias.bg-*undefinedbg
intl.hyphenation-alias.bsundefinedsh
intl.hyphenation-alias.bs-*undefinedsh
intl.hyphenation-alias.ca-*undefinedca
intl.hyphenation-alias.cy-*undefinedcy
intl.hyphenation-alias.da-*undefinedda
intl.hyphenation-alias.deundefinedde-1996
intl.hyphenation-alias.de-*undefinedde-1996
intl.hyphenation-alias.de-CH-*undefinedde-CH
intl.hyphenation-alias.de-DE-1901undefinedde-1901
intl.hyphenation-alias.eo-*undefinedeo
intl.hyphenation-alias.es-*undefinedes
intl.hyphenation-alias.et-*undefinedet
intl.hyphenation-alias.fi-*undefinedfi
intl.hyphenation-alias.fr-*undefinedfr
intl.hyphenation-alias.gl-*undefinedgl
intl.hyphenation-alias.hr-*undefinedhr
intl.hyphenation-alias.hsb-*undefinedhsb
intl.hyphenation-alias.ia-*undefinedia
intl.hyphenation-alias.is-*undefinedis
intl.hyphenation-alias.kmr-*undefinedkmr
intl.hyphenation-alias.la-*undefinedla
intl.hyphenation-alias.lt-*undefinedlt
intl.hyphenation-alias.mn-*undefinedmn
intl.hyphenation-alias.nb-*undefinednb
intl.hyphenation-alias.nl-*undefinednl
intl.hyphenation-alias.nn-*undefinednn
intl.hyphenation-alias.noundefinednb
intl.hyphenation-alias.no-*undefinednb
intl.hyphenation-alias.pt-*undefinedpt
intl.hyphenation-alias.ru-*undefinedru
intl.hyphenation-alias.sh-*undefinedsh
intl.hyphenation-alias.sl-*undefinedsl
intl.hyphenation-alias.srundefinedsh
intl.hyphenation-alias.sr-*undefinedsh
intl.hyphenation-alias.sv-*undefinedsv
intl.hyphenation-alias.uk-*undefineduk
javascript.options.gc_on_memory_pressureundefinedtrue
layout.3d-transforms.enabledundefinedfalse
network.websocket.allowInsecureFromHTTPSundefinedfalse
network.websocket.extensions.stream-deflatetruefalse
security.enable_ssl2falseundefined
security.ssl2.des_64falseundefined
security.ssl2.des_ede3_192falseundefined
security.ssl2.rc2_128falseundefined
security.ssl2.rc2_40falseundefined
security.ssl2.rc4_128falseundefined
security.ssl2.rc4_40falseundefined
services.sync.scheduler.singleDeviceInterval864003600