This is probably the most useful Firefox extension that I’ve come across in recent months! Resizeable Textarea is an extension that allows you to interactively resize any textarea on a web page.
Simply drag your mouse over the bottom or right edge of the textarea and drag to resize. How often are you in a forum or on a site that provides you with a text field in which you are meant to type, but then leaves you with only half a dozen lines to see what exactly it is you are writing? This lightweight extension is a great way to get around this inconvenience.