Like dblohm7 said, the issue here is when something besides the currently running instance of Firefox does an update. This can happen with the Linux distro packages or if you open Firefox with multiple profiles at the same time. I know it is a big pain, but hopefully this at least helps you understand what is going on.

If you choose "restore previous session" under general preferences, then you can at least not lose the set of open tabs when you restart.

As for 2, Firefox already does this, and has for about 4 years. Since those comments in 2008 and 2015, Firefox has shipped the Electrolysis project, which makes Firefox multi process. The UI (mostly) runs in a different process, which massively improved UI responsiveness, because janky websites can't interfere with clicking on stuff in the UI. One web site crashing can still cause another web site to crash, if it happens to be in the same process (out of 8) but we're hard at work on the Fission project which will move individual website domains into their own process. Though you can still end up with one instance of Google Docs crashing and taking down another one.