Firefox doesn't present it in a readable form (the page width is so large that reading the text is annoying). Which browsers handle this well?
resource:///defaults/profile/chrome/userContent-example.css
the file goes in <profile directory>/chrome/userContent.css. On a conventionally installed Firefox on OS X, the profile directory is: ~/Library/Application Support/Firefox/Profiles/<random characters>.default/
You may have to create your own "chrome" subfolder in there. (I did.) Some poking around reveals that the essays on Paul Graham's website achieve their indentation by sticking all the text in a <td width=455>. 455 pixels, then. So I tried this CSS file, having spent all of three or so minutes looking at a CSS reference: ~ $ cat heh.css
p {max-width:455px}
And installed that as <profile-dir>/chrome/userContent.css. ... This seems to have far-reaching implications. It does make all the paragraphs on this website, except for the first one, fit in what is presumably a 455px box. This also goes for Hacker News comments, and it also constricts the paragraphs on a website that pretty certainly has its own CSS. I suspect the only thing that would override this is a CSS that specifically changed the max-width property of <p> objects. (I expect a CSS expert would have been able to predict all of the above, except possibly the fact that it seems common for the first paragraph to not be in a <p> tag.) Oh, and I had to restart Firefox for the effects to be visible; and, editing that CSS file, it seems I'll have to restart Firefox again to see changes.For those who don't want to go to the above effort to see the results: http://imgur.com/F1MHng3 http://imgur.com/jYly4fX