I\'ve made myself a bookmarklet, and it functions just fine, but when added to a toolbar in Opera or Firefox, it just takes on the default bookmark icon for the browser (a g
That's not quite right: A bookmarklet has no domain, but it has a location (which is the bookmarklet itself) and you can assign an icon to that. After that it's a matter of how the browser saves icons (Firefox saves a bookmark's icon permanently, you may not be so lucky with other browsers).
P.S. Security doesn't even play into it, icons can come from anywhere. There is no restriction.
See http://www.tapper-ware.net/blog/?p=97