Now here is my solution: Resizeable Textarea extension. It lets you resize most of those textareas.
Firefox 4 with build in resizing is out!
Use it, this Extension will be no longer supported and developed.
Justin Watt made a extended version "Resizeable Form Fields", but because i work on a completely different solution, to get rid of the flaws of 0.1a, i will not support development based on the old code.