Rated 4 out of 5 stars

I tried to follow the advice of 90c846, but Thunderbird wouldn't install a 'corrupted' file! Instead, I've installed an older version of Thunderbird, which is fine, as I just want access to my sieve settings without manually going into my remote server and editing the file!

Only 4 stars, as the extension really should be keeping up with versions of Thunderbird!