Hey there:
If your extension loaded this page, then it needs your help.
You see, because Backup Brain is self-hosted. I can’t know in advance where to point it at to save your bookmarks. Please open the extension’s preferences and enter the address of your Backup Brain.
If it’s on the same computer as your browser this is probably just
http://127.0.0.1:3334
or
http://localhost:3334
If you’re still having trouble please file a ticket. Include the name and version of your web browser, a description of the problem, and a screenshot if possible.
I’m happy to help out on the fediverse too.
-Kay