Using Firefox Quantum 60.8.0esr and Thunderbird 78.3.1 on RHEL6, any attempt to 'email link' from Firefox that should open Thunderbird results in:
Thunderbird is already running, but is not responding. To use Thunderbird, you must first close the existing Thunderbird process, restart your device, or use a different profile.
This is new since the recent thunderbird-78.3.1-1.el6_10.x86_64 update.
Any thoughts on where I might look for help?