How can one regulate OpenType features in text (relevant to gecko used in Thunderbird mostly)

Hi, 

I was having issues with Thunderbird 3.x applying undersired OpenType 
features to text without any way to control which features to apply to which
bits of text, and which to apply by default. After asking about this on 
mozillazine in the Thunderbird section, I was directed here, since it looked
to be something relating to Gecko 2.0 

If anyone knows how to selectively enable/disable these features (or just 
turn all of them on/off), could they reveal how this might be achieved? 
Hopefully this it the right place to ask; if not, hopefully someone here 
knows what IS the right place to ask =) 

- Mike "Pomax" Kamermans 
nihongoresources.com