Since I've been with Firefox since Phoenix 0.1, I'll let you in on my config.
*Themes:
+Crystal Dream (Currently Used)
+Black Japan
+iPox
+Metal Lion Brushed iCe
+iFox Graphite
+Metal Lion iCe
*Extensions:
+ Talkback (Crash reporting)
+ Fasterfox (Broadband Firefox Optimization)
+ Adblock (Obvious)
+ Adblock Filterset.G Updater (Updates the Adblock filters.)
+ Sessionsaver .2 (Restores tabs upon crash.)
+ Cute Menus 2 (Puts little icons next to close, etc. Supported by most all themes)
+ Coralize (Coral Mirror plugin, for dead webpages)
+ DownThemAll! (Mass downloader)
+ Chatzilla (IRC)
+ Buttoner (Allows install of Themes saved as .jar files on HDD.)
+ Sun Cult (Shows sun and moon phases. Very handy for us Pagan types.)
+ IM Translator (Allows for translation via Copy/Paste)
+ LeetKey - Disabled, enabled only if I run into a dumbass with unr34l3 type.
+ Homeland Securtity threat level - Disabled, it never was useful.
+ Slashdotter (Slashdot.org specific plugin)
+ Duplicate tab (Obvious)
+ Download statusbar (Puts downloads in a small tidy statusbar, instead of DL manager)
+ PDF Download (Download PDF, or view as HTML - Adobe plugin is slow to read PDF from Web.)
+ Nightly Tester Tools (Force extension to install, as most incompatables are just a misset version number)
+ Firesomething (Make your own toolbar name for Firefox. Mine says Phoenix as that orig. name for Firefox)
+Flat Bookmark Editing (Self explanatory)
+ Open Book (Customize 'Add Bookmark' dialog.
+ FoxLingo (Whole webpage translation)
+ Resurect Pages (Bring dead pages back to life - sometimes.)
There ya go. All themes and extentions are available from the 'Get more Themes/Extensions' links in Firefox
This is just my 'Who's who of Firefox post'
BTW, if you don't have [Adblock|Adblock Plus] and Filterset Updater.g, GET THEM NOW!