Not sure which Firefox version turned on compressed session store, but seemingly have a situation where not only did the current file not get written in a format LZ4
tools can decompress, but also the backup files that I know are supposed to exist, be existing (which should be in a better state).
A plaintext file when these files get corrupted (rare in my experience, mind you) is REALLY helpful in these situations, and am fine with the performance degradation that I trust led to this design decision.
Have searched a number of variables in about:config
without luck. Don't tell me I have to fork each new version to edit the code and remove this feature that should be an option!