Unintuitive messages when starting with a non-existent profile directory

Binary package hint: mozilla-thunderbird

Setup
====
 you have a profile referring to a non existing directory (for example if your ~/.mozilla-thunderbird/profiles.ini is as follows:
------------------------------8<-------------------------------
[General]
StartWithLastProfile=1

[Profile0]
Name=default
IsRelative=1
Path=3yt5q2x7.default
Default=1

[Profile1]
Name=foobar
IsRelative=1
Path=35l08sbb.nosuchdir
------------------------------8<-------------------------------

And ~/.mozilla-thunderbird/35l08sbb.nosuchdir does not exist

Unexpected behavior 1
==============
If you start thunderbird with:
   $ thunderbird -P foobar
you will get the following warning message window:

>>Thunderbird is already running,but is not responding. To open a new window,you must first
>> close the existing Thunderbird process,or restart your system.
>> OK

Unexpected behavior 2
==============
If you start thunderbird with:
   $ thunderbird -ProfileManager
and explicitely ask for profile "foobar"
You will get the following warning message window:

>> Thunderbird cannot use the profile "foobar" because it is in use.
>> To continue,close the running instance of Thunderbird or choose a different profile.
>> OK

Suggestion
=======
It would be better to say that the directory does not exist !!
This is particularly frustrating, if you happen to have a profile whose directory ends with the space. No idea how the guy who reported the problem to me produced a directory ending with a space but I observed it.

Thank you for your bug report. This bug has been reported to the developers of the software. You can track it and make comments at: https://bugzilla.mozilla.org/show_bug.cgi?id=480309

Also changing the bug package to thunderbird, since the mozilla-thunderbird package is now a transitional package to the thunderbird package.