Hm actually I can almost repro on Linux: I can use the browser but I can't close the tab running code. This seems non-ideal. Maybe there is a better bug for this but you should always be able to close a badly performing tab.

TabStrip is for tab UI stuff; in this case the TabStrip is functional (sends close requests), the problem is in the code below that (e.g. the renderer not being responsive to such requests).  I don't know what the right component is for such issues :/

Hm I have a test site here [1] where I can only reproduce when devtools is open. This seems intentional here:
https://cs.chromium.org/chromium/src/chrome/browser/ui/fast_unload_controller.cc?rcl=da92021743d369b000d9c294337d2f900780dd51&l=58

Without devtools open, the tab closes within a few seconds. mozti4.1: can you reproduce without devtools open?

[1] https://cr.kungfoo.net/hung-renderer/big-int-computation.html

No, I can't. It's only freeze when devtools opened. Btw when devtools closed and computation processing i can't open it.

Punting to devtools team, but this is lower priority since it probably only affects developers.

Opening devtools also requires communication with the renderer main thread I guess, so it makes sense that you can't open it if the main thread is completely busy.

Devtools folks: Why can't we fast-shutdown a page that is being inspected?

If it is reproducible only when DevTools is shown then you can use following steps to kill any JavaScript:
1. request pause.
2. terminate current JavaScript execution.

GIF: https://twitter.com/ak_239/status/979767841573359618