I have Dyslexia and recently started using fonts for the disorder on my PC and e-reader.  This increased my reading speed dramatically with better retention.  Kind of a big deal for me as I use the PC & web lot.
   Others and myself figured out how to change fonts in Firefox but Thunderbird is different.  After changing Tbird's display formatting some incoming email is in the new Dyslexia font (so far all adds) but only a few corespondent emails, most are in the sender's original font. 
   Can you give instructions on how to change all my incoming email to the Dyslexia font?

Dear Mozilla Support, Monday 5-5th-2014 I have Dyslexia and recently started using fonts for the disorder on my PC and e-reader. This increased my reading speed dramatically with better retention. Kind of a big deal for me as I use the PC & web lot. Others and myself figured out how to change fonts in Firefox but Thunderbird is different. After changing Tbird's display formatting some incoming email is in the new Dyslexia font (so far all adds) but only a few corespondent emails, most are in the sender's original font. Can you give instructions on how to change all my incoming email to the Dyslexia font? Thanks for your help. Sincerely, ddbob.