I know that you can search for mp3's using this little trick:
http://www.tech-recipes.com/rx/851/google_find_free_mp3s_wmas_oggs_and_other_music_files/But is there any add-on for firefox that allows me to search for files from my search engines bar?
None.
google custom search. I don't know how to make an addon, but it's nothing a bookmark couldn't do. Personally, I don't use the search bar. The navigation bar is enough for me, since it performs the exact same way, except you can't easily change the site to search.
"Parliamentary inquiry, Mr. Chairman - do we have to call the Gentleman a gentleman if he's not one?"