Ah, looks like one has to fool with the maxversion...
The drill goes like this
1. Find the extension in the list and right click "source code" and save the
.xpi on your Desktop
2. Open the .xpi in the file-roller application by double clicking it
3. Extract install.rdf
4. Edit the maxversion string in it. Current Abrowser version is 21, so make
it (much) larger than that. (This way you won't have a problem with newer
versions) Save the modified file on Desktop.
5. Insert the modified file into the .xpi archive by drag&dropping it there
6. Install the .xpi by drag&dropping it onto a Abrowser window.
7. Restart browser
And bam! It works.
I've used this trick on many extensions and most of them work. It's a shame
they put in such a maxversion anyways... Maybe Trisquel should host a
maxversion bumped version of this extension locally to save people the
trouble of doing this themselves.
