I'm glad you noticed! We did indeed roll an improvement on Linux too, see: https://bugzilla.mozilla.org/show_bug.cgi?id=1771712

In a nutshell we're directing the OOM killer towards less interesting processes within Firefox so that when the system is low on memory they'll get killed first. This not only makes it more stable overall but it plays nicer with other applications too. Web pages that leak memory in the background are particularly likely to be killed by this mechanism and that alone is a huge improvement in overall stability.