I was wondering whether this “effect” is a known problem or it happens only to me:
As you can see the blank space looks like a small gray dot. I´d really like to remove that, but after trying multiple things including changing colors, fonts etc., I didnt find any solution.
When there is no space (see h4 in my example above) there is no “dot”.
I also made a picture in case you dont see the “gray dot” in the above example:

Edit: So it seems the problem is related to Firefox on Windows 7 (probably other versions too).
Edit 2: It is most probably a hardware-related problem, because it seems to only happen on computers with an ATI graphic card. I will keep you updated and so long mark BoltClock´s answer.
Confirmed on Firefox 8 on Windows 7. Doesn’t affect Firefox 8 on my Mac, nor can I reproduce it on earlier versions of Firefox…
Since it isn’t appearing on anything but Firefox 8 on Windows, you may wish to report this as a bug. Include a link to your jsFiddle demo, as well as your screenshot.
Start here: https://bugzilla.mozilla.org/enter_bug.cgi