I'm relatively new to writing userscripts (I've never had any education on using javascript either) and I've run into a problem I just can't find a solution to so I was hoping you guys could help.
I believe this is because getElementById doesn't pick up hidden elements?
If you need more or clearer information please ask.
Examples:

not working on ff with gm -

working on chrome -

working on ff with gm on reply to page -