Rated 5 out of 5 stars

To get past the problem I simply edited the .XPI

Open the .XPI with any "zip" utility and extract the install.rdf. Open install.rdf with you favourite text editor and find maxVersion and change to suit. update the updated install.rdf into the .xpi file.

Note that the button does not work, but adding the NotTo, NotCc or NotBcc to the email seems to work.

As always use at your own risk :)