I get that Chrome like rendering in every browser on my tablet (1) and with Opera and the stock browser on the phone. I reinstalled Firefox on the browser and it looks like your one. I understand that it makes difficult to follow threads but at least we can see deeply nested comments: they don't collapse to a single column of letters.

(1) Lines are not terminated at the screen boundary on the tablet if I zoom in. They keep going off screen to the right. Same on the stock browser on the phone and with Opera if I turn off text reflow.