Rated 5 out of 5 stars
It works on Firefox 3.0.11.
If it was not installed, try the next...
1.Extract an install.rdf and a chrome folder from resizeable_textarea-0.1d-fx.xpi.
2.Open install.rdf by the text editor.
3.Change the number of the version in the next part.
4.ZIP compresses an install.rdf and a chrome folder.
5.Change the name from resizeable_textarea-0.1d-fx.zip to resizeable_textarea-0.1d-fx.xpi.