How do I enable overlay scrollbars in Firefox?

Solution 1:

That is currently not possible, due to the libraries that Firefox's user interface is written using.

There is a bug report that you can mark as affecting you: https://bugs.launchpad.net/firefox/+bug/767040

Solution 2:

If the intent is to improve contrast for the existing Firefox scrollbar (not the overlay), a workaround is available in the form of an add-on which has been reviewed here and is available via from the official Firefox add-ons page. To quote from there: "This add-on is mainly for people, who want different "high contrast" scrollbars for their default Firefox theme. These scrollbars can be more kindly for eyes".

I don't use that add-on since I already have the Stylish add-on installed: this add-on allows one to modify scrollbars. My simplistic tweak is in the comments section of the first link.

Solution 3:

This works well in 11.10. Try it in 11.04.

I've tried it in 12.04; it does change the size, but not the color.