I don't think you should say "Keep Thunderbird Alive" when asking for donations because it sounds like it's in peril.
Businesses want to use a stable email application that's not in peril. They don't have to worry about Outlook going away or being abandoned.
Start showing how many users you have and make people feel like the number of users is growing and that TB will be around for a long time because everyone wants it and everyone contributes to it's growth.
