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)
:)

Rated 5 out of 5 stars

Same issue with Firefox 40+
Any changes made in the editor do not appear when closing and reopening FF and have to be reset manually every time.
Hopefully this can be fixed, this addon is one of the main reasons I use FF. Still gets a 5 star rating from me, I just hope this issue can soon be fixed.