That sorted it for me - thank you very much ! However, I'm not sure if it's related, but the fonts in my Thunderbird 3 immediately went haywire. I'll change back that line and see what happens.... erm, still wonky, bah.
Thunderbird 3.0 fonts still show fine for me but my install may be different from yours. I installed TB3 by downloading the tarball directly from Mozilla and extracting it into it's own folder in my Home directory. I then changed the command path in the menu items for TB 3.0. Once I started TB3 I set it as default and it was done.
On your font problem, try this:
First, go into "about.config" and search for "layout.css.dpi" and set the value to "0" (default is "-1") Then shutdown TB but don't restart yet. Here's the reference for the setting and what it does:
Go into System Settings/Appearance/Fonts and make sure that "Force fonts DPI:" is set to "Disabled". Hit "Apply" and close.
Now start up TB and check your fonts. They should not only be back to normal but should be following system settings for fonts rather than it using it's own (unalterable) chrome settings.
This should work for Firefox 3.6 as well.