Thank you for fixing the error.
Do you think it would help the performance issues as observed and reported in the pdf file (user story)?
Improving usage of Activity Manager would a must to provide basic info to end-user when something is processing in TB (loading email, loading calendar, indexing, copying, moving, sending email, looking for folder, etc... or any action that would cause a blue wheel in the title bar).
This would help to provide a hint what to look for when something goes wrong... then you could also have console log/info or else to indicate the issue (it is great by the way that smtp issues are now logged in the console, much more accessible). Finally Firefox provide the about:performance (aka Task Manager) and about:serviceworkers both accessible via the Troubleshooting page... which may also be handy to populate with what Thunderbird is doing... are those in use? When I look it all seems empty...
It could be a start to better processing transparency in TB... which is a great benefit of using open source software... you can always know what they do... especially when something goes wrong... to help report it... and have it fixed...at some point :-)