@Ivaylo Valkov The trick is having nothing but "%s" after "?search_query=".

It might be easier to just add YouTube to your Firefox's search, if it isn't already, and then go to "Manage Search Engines..." select YouTube and click "Edit Keyword..." make the keyword !yp.

Then entering "!yp mickey my friend" will kick you to YouTube results containing an awesome remix.

If you're having trouble getting it to work, others probably do too, that alone is a good enough reason for your extension to exist :-]