@Ivaylo Valkov How you described what your extension does perfectly matches what the bookmark approach I mentioned does. If you have YouTube search bookmarked with the keyword !yp, then if you enter "!yp lolcats" in the address bar it will redirect you to a YouTube search for lolcats. The "!yp" of course has to be at the start.

Perhaps your extension allows "!yp" to appear anywhere in the string, or maybe allows you to specify multiple like "lolcats !yp !goog !wiki" and be redirected to all of those searches.

Maybe I'm misunderstanding something (very possible), but I don't see how your extension provides something Firefox didn't already have.