Search in side the bookmarks

First way =>

You can bookmark your bookmark page,
see all the bookmarks , are stored in html page.,
For example in my system the path to bookmarks page is
/home/narendra/.mozilla/firefox/5h9delrl.default/bookmarks.html
so open it in web browser,
like this,
Now press Ctrl+F and now you can search any bookmarks.
there is one good feature about the highlighting, so you can just click on highlight and scroll to see, (no need to click on next and next)

2 nd way

Google toolbar provide the way you can search
see this window , you can see it,