Hmm, okay. FYI Sinon 10 does work fine in Firefox 60, what we're dealing with here is the use of RegExp's capture groups that is only supported in ES2018+ and therefore you may consider updating that compatibility page to remove the mention of ES2017 😃
Hmm ... true, that is a bit confusing. The source version of ES is more about what kind of syntax contributors can write, but totally agree it's unfortunate. The supported runtimes still hold, of course, but maybe we should write ES2018. @mroderick ?
TBH, i don't think it is worth bumping the ES version requirement of Sinon just because that single package is using something it does not really requires (as i told them in their repo), this is just causing troubles unnecessarily, IMHO.
We're using Firefox 60 ESR to run our Karma tests since that is the lowest Firefox version we do require to support at my company's website. So yeah we're prepared for it, but when there is a good reason - we would also like to use latest versions of all packages as the way to get security advisories sorted.