Back when this functionality wasn't native to FF, Resizeable Textarea gave you a positively un-claustrophopic feeling. It was as if the web had opened up, and you suddenly had a lot more space to move; or like you had come to the top of a hill, and the view was extending before you
Having a quick indication of how the line wrapping would look like in the final post, oversight over what you'd written, finding mistakes and redundant pieces of text; especially for someone like me who likes to write long posts and edits them many times for better style and impact before posting, this extension was a life-saver.
I never got into the whole review writing game before, but now that I have, writing one for one of my favourite extensions was a must, discontinued or not. Besides, I don't know if the extension needs to be obsolete, I've only just abandoned FF3 for higher versions, and frankly am unimpressed with the native resizing. Right now for example, the text area I'm typing this into is extended over some text beside it, and it shows through, interfering with my writing. Resizable Textarea is still a top-ranking add-on IMO and I'm sad to let it go.
EDIT: Oh and I'm on FF 6.0.2 now, if it matters. I didn't have Internet for a long while, so I completely jumped over FF4 and 5.
P.S.Oh great, AND the resized text field goes UNDER the vote stats to the right here. RT, come back.