[CentOS] Thunderbird: can't seem to install french spell checker

Hi,

I can't install a french spell checker in Thunderbird. There's a link in 
Thunderbird's preferences, to download new dictionaries, but it's dumb. 
So I downloaded the dictionary manually (spell-FR.xpi) and installed it 
in Thunderbird using the 'Extensions' dialog. But the installed 
dictionary doesn't appear anywhere.

Googled some over this problem, and it seems like this happens to quite 
some people.

Anyone on this list successfully installed a non-english spell checker 
in Thunderbird?

Cheers,

Niki