Not sure when this started, but with the latest version of Firefox Nightly, STG has a "Legacy" label and clicking on the add-on or the options takes me to a blank screen. Still works as expected, and I am able to go to the manage groups screen.

Yes, I saw this message, but I have no idea why it appeared. Also, I can not find anything connected with it on the Internet. If you have information about what it is, please tell me about it. Thanks.
Regression from nightly. The latest Nightly is fixed now.
Source: https://bugzilla.mozilla.org/show_bug.cgi?id=1531658
Yes, it was a problem with nightly. Everything seems normal now. Thank you for the very useful extension.
Thanks guys!