And in another computer I would have to delete manually this lock file in order to use default profile... Any suggestions?
When you have the problem, run from the command-line: ps aux|grep -i thunderbird
to see if any instances of thunderbird remain. If so (and I suspect that this is your problem), issue from the command-line: kill -9
No, program is closed nicely... Lock still remains.
I repeat, don't use "kill -9". It's rarely necessary and when it is it's a sign of a problem. Use plain old "kill" so that target processes have a chance to do their clean-up (lock file removal, e.g.). If that doesn't lead to the program's termination, then you can try "kill -9".
Well, I close programs from cross in the upper right corner... Is it OK? :) And after I close it, ps ax shows no Firefox/Thunderbird anymore.