I think you are correct. Looking into it I got stuff battened down so much I't hard to figure out what to do. Got, due to advice on BG in the past, all kinds of adblockers, SSL only, https 'anywhere', uBlock, and also my FF settings with all locked down, no sharing, histories, bookmarks,cookies, etc! Ha. Paranoid much, I ask myself?
Albrecht, I run two security addons on FFx - NoScript, and RequestPolicy.
They handle everything and they are really fine grained. Get rid of everything else, they are more than likely interfering with each other. (uBlock is notorious for this)
I've hit those errors you've mentioned too.
'sudo apt-get update && sudo apt-get upgrade' or 'sudo apt update && sudo apt upgrade'
Your security certificates are outdated.
It's not that your security is too tight.
Https-Everywhere is a good addon - if you are running straight FFx, go ahead and keep it. It will cause problems on certain sites that are http only, though.
Security comes at a cost - and the cost is usually that you have to learn how the addons work, or avoid certain sites. But the advantages are you don't have to worry about drive-by downloads, or ransom-ware.
