If Mozilla gets blocked, people would just install some other browser (probably, something from Russia). I do not see how this helps anyone but the government itself. And departure of hundreds (if not thousands) of western companies did nothing to the Russian government, some problems with a browser with almost non-existent userbase would have the same effect. It should be quite clear by now that such tactic simply does not work.
VPNs are not categorically banned in Russia either. Just 95% of them. Categorical ban is not actually required here. Government can just create licensing procedure and license only those VPNs, which follow “rules”. I do not see how this is different from ISP bans.
As a guy from Russia, I must admit that vpns are not a big problem for censors. They can be easily blocked, including self-hosted ones by protocol detection. And DNS would not do much with IP and clienthello-based blocks. And most users are not enough tech-savvy to constantly switch to new protocols as old ones get blocked.
Ukraine use ads for anti-putin propaganda. So the russian goverment told Google to moderate ads, or all Google services will be banned. Google decided to just disable ads in Russia completely.
Alternative solution: Since YouTube disabled all ads in Russia, you can just use russian vpn/proxy for the most effective YouTube adblocking possible.
If xmpp and matrix are included, why not include email?