I have exactly this problem. Self hosting on Synology, something happened with My firefox and it refreshed which means I have to log back into the bitwarden addon. When I try it gives me a “networkerror when attempting to fetch resource” message. I can log onto bitwarden via the Browser itself just not the addon. Tried uninstalling the addon and reinstalling to no avail. I read that its certifcate related and have tried the create a new etc as per original poster - again with no success. Was there ever a solution to this??