Rated 1 out of 5 stars

Waiting the new update you can use this method for installing this add-on.
Go to this site : http://mozmonkey.com/copyplaintext/#install, select download and save the file in your desktop.
Rename xxx.xpi --> xxx.zip, open the file and extract "install.rdf", search this line "em:maxVersion="3.0.*" and replace the 0 by 5, save, put the "install.rdf" modified in the zip, rename xxx.zip --> xxx.xpi and drag in Firefox.
I tested and it's run corretly with Autocopy 1.0