I also restarted CI on 2ab427e before the last 3 commits, to see what happens. It was previously green.

Okay I think the failures of these

test_string_conversion[firefox]
test_bigint_conversions[firefox]
test_hyp_py2js2py[firefox]

on the rerun of 2ab427e demonstrates that my recent changes to string and bigint conversion aren't actually implicated in the timeouts...

Yes, as much as I like CircleCI, I think it might be time to evaluate an alternative CI provider to see if we also get such issues there. I'll try to setup Azure pipelines which have 10 parallel builds and unlimited CI minutes (though I'm not very fond of their UI).

It might still be worth investigating Github Actions in #1690 in the future but for now CI appears to be green again.

Or at least I did see green CI in #1684 which included all of these commits.