Rated 5 out of 5 stars

Found the fix for Firefox 40+

go here:
http://menueditor.mozdev.org/
click on "install version 1.2.7 for Firefox 3.x and Firefox 4"
then uninstall Menu Mod II from your addons list...
mod should work normally again (it does on my end now)
:)

This user has a previous review of this add-on.