Comment 5 for bug 308605

Following bug are found by search for "profile already running".
> Bug 278860 confusing "profile in use"/"already running" error when profile is missing (not found)
> Bug 381139 Confusing "Thunderbird is already running..." message when profile is read-only.
> Bug 459991 "Already running" message if profile directory doesn't exist

Your case is 4-th case : "profile is in use".