Firefox simply loads the page without complaint, just mentions that it's "not secure" and puts a broken lock icon in the addressbar.
Firefox is nice.
On the other hand, if a page has HSTS Firefox absolutely won't let you see the page under any circumstances no matter what, whereas Chrome at least has a hidden `thisisunsafe` bypass.
I used Firefox as my daily driver for 15 years. Switched to chrome a couple months ago to see what the fuss was about.
I am shocked at how glitchy chrome is in comparison, with the likes of crashed dev tools panels and tabs that just dont come back properly after being idled being a regular thing.
I will be returning to Firefox before long I am sure of it.