I would like to make a derivative software program from both Mozilla Firefox and Mozilla Thunderbird. Basically, the new program would be both a Web client and an e-mail client. I need to use the most stable latest and greatest source code for both Firefox and Thunderbird to make one derivative application that has and “mashes up” the features and functionality of both of them. I would rather base my new program on release code rather than any development/experimental/unstable code. I don’t think that I can use SeaMonkey (the “Mozilla Suite”) because it seems to be outdated and behind in supporting modern Internet/Web infrastructure; for this reason, my understanding is that I need to base off of Firefox and Thunderbird in order to get the best and most current Web and e-mail client support.
What is the best known method for going about this? Is there a particular Mozilla source code branch that contains the latest release-caliber material for both Firefox and Thunderbird, in some kind of unified manner? Or, is the release code for each of the two applications inherently diverged from the other, and would I need to take the separate release source tree of each of them and unify them myself from scratch?