Existem imensas sugestões aqui para o fazer
Two fixes that I'm not happy with: 1) make a copy of the thunderbird.exe and rename it thunderburd.exe. Have one profile point to this copy. Works, but I have to remember to manually update the copy. 2) create a task in task scheduler and run the task link. Works, but it takes half a second longer to run and a DOS box pops up for a second as the program starts.