Those bugs are all extension bugs. The built-in option to "clear data on exit" that Firefox has in about:preferences seems not affected by them. Although of course they should be fixed.

But it is affected. It's very easy to confirm that even with "Clear data on exit" activated, websites recognize you across sessions.

"Clear data on exit" means remove all traces of me visiting websites from my device. It has nothing to do with how the websites will operate if I decide to do so.

That could be due to fingerprinting, your IP address etc, which is much harder to anonymize.