GlassMyFox is Best I've seen!! Rated 5 out of 5 stars
I have reviewed this once but just have to tell ya, I love this!!
I would also like to suggest transparent scroll bar. I saw a reply to a post but there are no setting that I can find to set transparency level on the scroll bar.
It is not possible to modify main window scrollbars from a bootstrapped (restartless) extension like GMF. But
with "NewScrollbars" ( https://addons.mozilla.org/addon/noiascrollbars/versions/ ) you can set semitransparent default scrollbars (v1.0.3pre4+).