FireFox and UK spell checker

[kj <koffiejunkielistlurker@koffiejunkie.za.net>]

Hi guys,

In Firefox I have en-gb selected as my default language, but when I type 
in a text box, it still highlight according to US spelling.  I looked at 
about:config and found that spellchecker.dictionary is set to en-US.  I 
set this to en-gb, restart FF, and it's back on en-US.  I tried en-GB 
too, just in case.  I have gone as far as uninstalling "US English" 
under the languages section, all to no avail.

Does anyone know how to make en-gb stick?  This is driving me up the walls.

Thanks