You chose to install a plugin that modifies documents you see in your browser. You certainly have that right. But it's not anyone else's fault if that plugin modifies documents you see in your browser.

> You chose to install a plugin that modifies documents you see in your browser.

You are jumping to a conclusion on a mere speculation. The site works fine with uBO + default settings/filter lists. I could not even "break" the site using "medium mode", which blocks all 3rd-party scripts/frames.

Properly-formatted CSS shouldn't be broken by uBlock. Nor should properly-formatted HTML.

Well then, one of two things happened. Either you visited a site with improperly formed html or css, or uBlock doesn't work like it should.

Hmm, I also have uBlock Origin on, and the website renders perfectly for me (on chrome). I think this is might be a firefox specific issue.

It also renders fine in Firefox with default settings/filter lists.