this vulnerability is only really meaningful on multi-user systems
Well, that says it all. CPU manufacturers have no incentive at all to secure the computations of multiple users on a single CPU (or cores on the same die)... why would they? They make more cash if everyone has to buy their own complete unit, and they can outsource security issues to 'the network' or 'the cloud'...
Years ago when I was in University this would have been a deathblow to the entire product line, as multi-user systems were the norm. Students logged into the same machines to do their assignments, employees logged into the same company servers for daily tasks.
I guess that isn't such a thing any more. But wow, what a sh*tshow modern CPU architecture has become, if concern for performance has completely overridden proper process isolation and security. We can't even trust that a few different users on the same machine can be separated properly due to the design of the CPU itself?

Seamonkey (Mozilla browser/email/news suite) still exists! https://www.seamonkey-project.org/dev/
And there's even still a build of uBlock Origin for it! https://github.com/gorhill/uBlock/
There is still hope, if we keep the open tools alive...
Posted from freshly-installed Seamonkey browser with uBlock Origin :)