This is probably referring to some work to use Stencil for self-hosted code. That reduced process overhead by 6%, which is quite a bit: https://bugzilla.mozilla.org/show_bug.cgi?id=1688794
There might have been some other Stencil work that landed in 92 to reduce memory.
There's a description of what Stencil is, and some work related to it that landed in Firefox 90 and 91, here: https://spidermonkey.dev/blog/2021/07/19/newsletter-firefox-...
I believe this refers to the constellation of work surrounding the ReShape hidden class datastructure refactoring https://bugzilla.mozilla.org/show_bug.cgi?id=reshape
There was an initial change and then various bits of followup work to take advantage of it.
(Ah. mccr8 says it's Stencil. That probably makes more sense.)
I'm interested as well since they had a layoff of the Servo team. Did they rebuild that team with unannounced hires? Outside contributions?
Servo has very little to do with JavaScript, so no.
The parts of Servo that made it into Firefox are still being worked on by Firefox developers. I don't know how much activity is happening on the now-external Servo project itself.
I went back the last few versions major release notes and didn’t see mention of the initial work to improve the JavaScript memory management. Is anyone aware of this work/what’s going on to improve memory management here? Interested to read more about the technicals!