This is something I've seen on an old forum I used to frequent and thought it may be of interest around here, I'm not trying to get gpforums to use it or anything, just some food for thought so don't jump on me.

I used to frequent www.gotgames.com.au and they used to have an option up the top where you could check and see who has quoted you, it was quite good for keeping track of conversations, especially good when you're needing help with something.

Just thought I'd bring it up

INB4 EgorBB etc

Use this until EgorBB arrives.

Should be do-able with javascript?
Pull the username from td.mastheadUserText.innerHTML: <div><strong>Username</strong></div>
Quote headers are stored in td.titles - font.small - b, search all of those on the page, compare against username, set focus on that post if a match is found.

Firefox extension in 3...

Lol, Jesus, no. Not a Firefox extension for that. Fx extensions are evil. Just write a Greasemonkey script, you can insert a little search form into each page, do a search like you say based on its input, and then scroll to it.

"Extension of an extension" then.