[ubuntu-uk] thunderbird fonts

[Norman Silverstone]

I have asked this question on another users group but so far, I have not 
had an answer which works. Using Thunderbird 12.0.1 and Xubuntu 12.04 
32-bit plain text the font in the message window is very small and I 
want to make it larger. I have tried making changes using Edit -> 
Preferences -> Display -> Formatting -> Advanced but nothing changes. I 
assume I am missing something but I don't know what. I have tried Google 
but I am more confused than ever. Could someone, please, be kind enough 
to point me to where I might find the answer to the problem. Thanks

Norman