Apologies to non-Firefox users. The original Resizable Textarea extension for Firefox ... does not work with the latest version of Firefox. After missing it for months, I decided to do a search to see if an updated version existed somewhere... Sure enough, it does. I am currently writing a description in a textarea (the rectangular white region where you put your comments on Mofi or even, heavens forbid, on MeFi) that is as wide as my computer screen. No more scrolling to see an entire comment while editing :-) Sadly, it does not seem to work with gmail nor with google groups.
Resizable Textarea extension for Firefox