Might require static analysis to find all cases where JS-version specific is used in the Mozilla codebase. If too numerous, might require automated rewriting.
Probably need to wait for some ES6 sugar to land before being able to do that.
for each() should be doable now, I guess.
As is harmony-style generators (i.e. function*)
To completely remove the version= parsing code from ScriptLoader we will have to finish this. I actually get very few matches for this on searchfox: https://searchfox.org/mozilla-central/search?q=%3B%5Cs*version%3D&case=false®exp=true&path=