This is really troubling. Mozilla should stand up for its values. If it gives in now, many other countries will start pressuring Mozilla to censor as well.
The inability to sideload unsigned extensions makes Mozilla a gatekeeper, which inevitably makes Mozilla a censor. Apple put itself in this position and routinely censors apps in China. Mozilla should have expected to be in this position and never should have made itself a gatekeeper. It’s worth rethinking the signing requirement.