New Ubuntu user. Whiching from Mozilla Firefox to Moxilla Thunderbird

[Jeffrey Holle]

I am a brand new and impressed Ubuntu user.
Succeeded to get my Mozilla Thunder bird components.
Now, when I click on a link embedded in an email within the 
Mozilla-Thunder bird mail client, I get Firefox.

My question is, what do I have to do to loose Firefox dependencies?
Hopefully globally, but if not possible, what do I have to do to 
Mozilla-Thunder bird mail client to get it to use Mozilla-Thunder bird 
browser?