Rated 2 out of 5 stars

Sorry to say, that this is the wrong way to select a random signature.

There is no reason to read one signature file and write to another signature file every few seconds, when the signature is only needed when writing a new message.

The right way would be to open a file with signatures and select one, when composing a new message.

Like Tagzilla does it:
http://tagzilla.mozdev.org

This review is for a previous version of the add-on (1.4).