Firefox's containers is also a poor man's version of Chrome profiles. I want completely separate _everything_. Firefox's Profiles is similar, but then you get warnings about Firefox already running when you click a link in a non-Firefox program.
These things are deal breakers for me.
Containers is solving a different problem than you have. If you have multiple profiles running, how do you want it to know which in profile to load the link? You could set your link helper in your OS to run Firefox with the --profile option, to pre-set it, if that's what you want.
This is the expected behavior.
Use about:profiles to launch a process with another profile
I don't have any issue with fonts in F30, do you have a picture illustrating the issue?
Roboto font at 14pt, 115 dpi, default antialiasing in Plasma
The font issue I linked in another reply: https://twitter.com/juantreminio/status/1137563286319316992
It enables subpixel font rendering.
I believe it's the Roboto font at small sizes that causes issues on Firefox.