[gcp]

>very rarely Firefox would crash

The feature stops (or reduces the likelyhood) of that happening. It literally is made to trigger in a situation where the alternative is to crash.

>So, if I want to disable this, I should set a big number to the browser.low_commit_space_threshold_mb pref in about:config, right?

This will ensure that you crash and have to reload all of your tabs instead of the oldest ones, yes :-)