I have taken your idea and adapted it for Mac OSX users. I have attached an OSX MoodleDoc's Search widget.
If you could come up with a square model, I would love to replace the current one .
I have taken the liberty to combine your idea with this tip on using Firefox keywords
Bookmark this page
Look up the properties page of this bookmark (see screenshot)
Give the bookmark the keyword
doc themesin the addressbar will load the documentation on themes.
The multiple search block uses the same syntax to add search engines to a Moodle block.
So if you want your teachers to be able to directly search the MoodleDocs from inside your schoolsite, just type the same link into the Link field of the block's configuration page:
and name it something like Moodle documentation...