In https://bugzilla.mozilla.org/show_bug.cgi?id=1942684, we added use counters to track existing use of Error.stack on the web. This telemetry has been in release for a while, and the results are stable.

Looking at the Error.stack getter data, it's almost certainly ok to require an [[ErrorData]] slot.

Looking at the Error.stack setter data, hardly anyone is using the setter, but most of those uses are on objects that don't have an [[ErrorData]] slot, and about 7 percent or so are calling the setter with a non-string argument.

Hopefully this data is useful in making decisions about the shape of the API. Unless I hear otherwise, I'm going to remove this telemetry in Firefox 142, I think it's served it's purpose.