To add to this, Hacker News does not display well in either Chrome for Android or Firefox for Android[0], so it's not like it's only Servo (or even only Firefox) that has issues.
That's a feature ("font boosting"). It's a total mystery to me how something working so badly could ship, especially since the Android Webkit fork had a similar feature working perfectly. But apparently it's of "acceptable quality" in Chrome https://bugs.webkit.org/show_bug.cgi?id=84186#c24
The basic problem is that it's hard to tell the difference between nested tables used for nested tabular content and nested tables being (ab)used for layout, as HN does.
Mobile browsers attempt to make content more prominent than navigation. This matters a lot on e.g. mobile news sites.
Unfortunately the algorithm they use breaks horribly on comment threads, because it decides that long comments are content, while short comments are not important. (At least, this is my deduction from seeing it in action.)
You'll see it on reddit, forum threads, and here on HN -- so this is not exactly a layout bug, but a problem with how Firefox/Chrome try to apply some simple semantics to web content.
Sadly true. That's why I'm not using Firefox on android despite using it on the desktop. They never got the right algorithm for font inflation (that's how they call it).
HN displays ok in Opera Android but mostly because Opera can reflow text on zoom. That fixes almost everything.
[0] Notice the inconsistent sizes of comments (which actually does not always even correlate with nested depth): https://www.dropbox.com/s/b47lhe3px83wq9j/2015-05-01%2019.29...