I’ve recently started using Firefox instead of Safari. My two leading problems are spell-checking and the fact that Firefox insists upon opening external links in a new window.
I finally a solution for spell-checking. Although it’s not nearly as nice as OS X’s system spell checker (which checks on the fly), this is an acceptable stop-gap solution. Long term I think I may have to go back to Safari though (if only PithHelmet would accept new rules from me, damnit).
As for external links opening in new windows, none of the existing solutions work in OS X. All tab manipulation extensions screw up bookmarks in OS X. Very disappointing.