As promised, I looked into it and did some testing. There's an old
trolling tactic of posting something excessively long (wide, actually)
so the browser expands the width of page beyond the width of the screen.
The result is a side-scrolling page that is difficult to read. The code
behind HN and most forum software have detection and mitigation for
these types of side-scrolling attacks. If you had found something that
was successfully blowing out the width of the page into a side-scroller
then that would be a HN bug worth reporting.

The screenshot below is with a slightly older Firefox version 18.0.2
using a newly created user profile, without any plug-ins or add-ons, so
everything is at default settings. The menu colors and green-on-black
text colors are due to how the underlying graphics toolkit (gtk) used by
firefox is configured on the system.

As you can tell from the image size, the display is running at 1920x1080
resolution, and although it doesn't matter, the screen is 18.5 inch
diagonal (408mm x 230mm).

http://www.designtools.org/pix/graycat01.png

The longest line displayed in the image is 250 characters when using
default browser settings and font (typeface) sizes. If you increase the
font size, you decrease the number of characters per line. For example
this image has 137 characters per line.

http://www.designtools.org/pix/graycat01a.png

Setting "Preferences -> Content -> Fonts & Colors -> Advanced Button ->
Minimum Font Size" can save your eyesight at the cost of making some
badly written websites look worse than usual.

If the default display is still too wide for your tastes when using a
larger font size, you have two options; (1) reduce the width of your
browser window, or (2) write a browser plugin or addon to reformat
everything to the way you want it.

HN allows for posting pre-formatted text in comments for when someone
wants to post source code. The reason is the typical re-wrapping of text
in a browser would make a real mess of source code formatting. To post
pre-formatted text (code) to HN, just insert two leading spaces at the
start of the pre-formatted lines. Unfortunately, this feature often gets
accidentally misused for things like quotes. An example of misuse is in
your own post:

https://news.ycombinator.com/item?id=8042618

You indented the URL to businessinsider.com with spaces, so it was
turned into pre-formatted text and was not rendered as a clickable URL.

If you're curious about formatting options on HN, they're listed here:

http://news.ycombinator.com/formatdoc

Since HN does not re-wrap the pre-formatted text, it can be wider than
the page, and would normally make a side-scrolling display, but by using
CSS, only the pre-formatted portion has a horizontal scroll bar. In the
image below, you can see how these "too-wide" lines are in their own
little scrollable boxes.

http://www.designtools.org/pix/graycat02.png

Side-scrolling little boxes of text might be annoying, but it's better
than making a mess of pre-formatted source code, so it's supposed to
work this way.

If for some reason you're not getting the little scrollable boxes for
the excessively long pre-formatted lines, then either your browser is
much older than mine (unlikely) or some configuration, plugin, or addon
you're using is making a mess of things. You can test this by creating a
new user profile in firefox.

You mentioned ms-office, so it seems you're still running ms-windows. I
think firefox on ms-windows creates a startup link to its profile
manager on installation, but if I'm wrong, just use the command line:

C:/> firefox -ProfileManager

If you're still seeing excessively long pre-formatted lines without
being in little scrollable boxes, then you'll need to update your web
browser.

If you're having trouble with something else (and I've totally
misunderstood you), then please post link to a screen capture image of
what you're seeing, or you could email it to me if you prefer.