There seems to be an issue where extensions don’t load on Firefox. I had posted this issue on Streamlabs support, since I believed it was just theirs. However; It seems to be all extensions. I know a few have this issue on Firefox as well.
They do load perfectly fine on Chrome browser so it isn’t my PC.
Running any extensions in Firefox? Retry without them
Running the latest version of Firefox? If not upgrade it
Are you on Firefox or Firefox quantum?
Did you try a cookie clearing just in case?