I have this issue on two computers. Both have been tested with fresh installs of both my OS and Firefox with no extensions, and then with extensions. Both have been connected to different networks. Antivirus has been enabled and disabled. Once the extension has been removed, Firefox no longer has the issue.
Every single suggestion from Windscribe support has been attempted with them eventually telling me that a new extension that would 'fix these problems' is in the works. I haven't just come on here to complain without having tried a thing and I don't appreciate the suggestion that I have.
Just because you haven't had the issue doesn't mean others have been so fortunate.