The CuteMenus Classic add-on I like very much.
It also works on current FF versions. (e.g. 3.6.24)
For this you need to ignore the add-on version limitation.
Install the add on "MR Tech Toolkit". Then you can install or re-activate CuteMenus Classic (or other add-ons).
For installation: In the installation add-on window activate the checkbox "Deactivate compatibility check (maxVersion)".
For re-activating: In the add-ons overview right click to CuteMenus Classic and click to "adjust compatibility" (or similar).
I still use Firefox 3, because I don't like the graphical Design of newer versions. (I tried them, but then I reinstalled FF 3.)