Enable Textarea Resize
A web feature I liked when it came was the ability to resize textboxes. Especially multi-line textboxes (<textarea></textarea>) have a tendency to be too small and this feature really helps there. To my disappointment I find that many websites disable this feature to favour design at the expense of usability.
To re-enable this I use the Stylebot extension for Chrome. I have added a rule to the global stylesheet (applies to all websites).
If you have a similar extension for other browsers, I’d like to hear about it. I tried to find one for Firefox, but the ones I found seemed to have been broken for a while, so I gave up on that.