We have a bunch of bugs similar to this, but they are all just kind of related like remove JS versions etc. This bug is about really sticking it to them. Have a look at http://kangax.github.io/compat-table/non-standard/ for a good overview.
We can add parser telemetry for these languages features (like bug 1102131). At some point, we might want to use web crawler data like httparchive.org for offline searches for uses of language features.
Some of these should get standardized, not removed. For example some of the Error bits.
(In reply to Please do not ask for reviews for a bit [:bz] from comment #2) > Some of these should get standardized, not removed. For example some of the > Error bits. If you think we can get away with changing our format of Error#stack, then we should absolutely align with IE and Chrome here: http://wiki.ecmascript.org/doku.php?id=strawman:error_stack