Lots of type work. It's easier to just place the search box next to the address bar, and customize the search engines a little. (I think youtube wasn't default)

With this you can also select a film title (anywhere in a page) right click and "Search IMCDb for"... No typing, no copy and paste, just 2 clicks and you're there.

I was doing that since long time with keywords actually.
Make a bookmark to this url: http://www.imcdb.org/movies.php?title=%s
put "imcdb" in the keyword field of the bookmark properties.
then you can search a movie by typing in your address bar "imcdb" followed by the movie title.

http://mycroft.mozdev.org/search-engines.html?category=31

...to search the IMCDB database directly with the little search box.

I looked for it several times in Firefox add-ons with no result, but found it here. (just click on imcdb and it will be added)
Thanks to "Steven"...