I got similar error messages since 117.x.x. It would happen on tabs with email services open (both Yahoo and Gmail), but other tabs were not affected. My windows 10 system said there was network connectivity. My network provider is T-Mobile Home Internet which uses cellular. After installing a VPN product, all upload/download speeds increased and I no longer am affected by this situation. Not sure if this applies to your case, but in my case it appeared to be a timing issue with FF not waiting long enough for a response.