InfoLister - lists all your extensions with one click - you can then save or paste the list to forums etc etc.
example:
*** Extensions (enabled: 20, disabled: 0; total: 20)
Adblock Plus 0.7.2.3
Back to Top 3.2.0
del.icio.us 1.2
deskCut 0.5.0.5
DOM Inspector 1.8.0.9
Fasterfox 2.0.0
Firefox Extension Backup Extension (FEBE) 4.0.4
FirefoxView 0.31.2.1
Greasemonkey 0.6.6.20061017.0
IE View 1.3.1
Image Zoom 0.2.7
ImageShack® Toolbar 1.0.0.27
InfoLister 0.9f
Linkification 1.3.0
McAfee SiteAdvisor 25.0
PlainOldFavorites 0.5.6
Smiley Xtra 4.1.0
StumbleUpon 2.89
Talkback 1.5.0.9
TinyUrl Creator 1.0.3