Rated 1 out of 5 stars

If you get this message when trying to install the add-on:

"Copy Plain Text 0.3.3 could not be installed because it is not compatible with Firefox 3.0.11."

After some research on Google, what worked for me was this:

1. Download the .xpi file (right-click on "Add to Firefox", Save Link As...)
2. Unzip the .xpi file and you will find install.rdf
3. Locate the entry for , beneath
4. Bump the version number by replacing 2.0 with 4.0
5. Save the changes. With the new .xpi file you should be able to install the add-on

Note: I do not know if this is risky, or if there are side effects, but it seems to work for me.