Their is a add-on call "toolbar buttons" that has a mail button that you choose the path so you can choose Thunderbird portable or a different portable email client you like. Here is the link for the add-on https://addons.mozilla.org/en-US/firefox/addon/2377/
yes nice, but, will that change and adjust the drive letter when this changes? Doubt.
Otto Sykora
Basel, Switzerland
Not sure if this helps or not but why not try using tools>options>applications and then point it to Thunderbird Portable as the mail default? This is built into FF
“Be who you are and say what you feel because those who mind don't matter and those who matter don't mind.” Dr. Seuss
it does not update drive letters of portable drives. So it has to be set by hand each time again.
Therefore my Q above.
Beside that, there were some issues with it some time ago, causing apparently some loops running somewhere and causing problems with memory etc. This might be cleared by now, but the problem with drive letters persists.
Otto Sykora
Basel, Switzerland