Created an attachment (id=8603) [details]
Error message displayed at Thunderbird startup

Thunderbird version 60.5.2 64-bit
QuickFolders 4.13.2
Windows 10 home 1809, build 18290

Windows and Thunderbird are both fresh installations. I'm adding extensions to
Thunderbird. I have installed QuickFilters, QuickFolders, and FiltaZilla as
well as others. When I start Thunderbird, I get the attached error message
popup with message, "ensureStyleSheetLoaded failed: InvalidAccessError: A
parameter or an operation is not supported by the underlying object". The error
console has the following message: 

The connection was refused when attempting to contact ws://127.0.0.1:12546/. 
(unknown)

After that, the message below is repeated every few seconds. I don't think it
is related, but include it for completeness.

Warning: ‘nsIOService::NewChannelFromURI()’ deprecated, please use
‘nsIOService::NewChannelFromURI2()’ session.js:273:38

This error is not fatal, as Thunderbird loads and functions. The popup occurs
at each startup, however, and is annoying. Please note that I tried to install
Console2 as you recommend, but it doesn't work with Tbird 60.

By the way, on this bug report form, your OS dropdown only lists Windows
through version 7.

*** This bug has been marked as a duplicate of bug 26646 ***