>The something like three gray dots with shade in the bottom right corner of every textarea on any page open in Firefox, which is the resize handle. You drag it around and it resizes the textarea. UT is one of the rare places where this is somehow disabled. Using Firebug I don't see anything in the stylesheet that would interfere with that, but then I don't really know what could.

Yes, this is blocked at the style sheet.

If you need larger message width, simply click on Options to increase the value.