I see what you mean. It appears that the drop-down which says "Summary" is pushing that block of content off to the right (sometimes you can see a sliver of it at the right edge of the page). That problem doesn't occur in the stock Android (2.3.4) browser.

If I use a Fennec useragent string in the User Agent Switcher extension, I can replicate the problem on a desktop browser (Firefox 13 beta 4). The drop-down is floated within a container that uses 100% of the width of the screen. The next element floats up alongside the <select> rather than dropping down beneath it because that next element doesn't have a specified width or minimum width.

StackOverflow can solve this problem by editing its CSS to include a clearing rule:

.inner-wrap {
 	padding: 5px;
	overflow: auto;
	clear: left;
}

However, as end users, I don't know whether there is anything we can do.

This problem has appeared in sites for years, and it seems unlikely that Firefox will change the way it handles floats to work around developers who forget to clear them. (Guessing as to what the developer must have wanted was something that IE did for years, but I think even Microsoft is starting to require developers to pay closer attention.)

Thanks, I submitted the problem to StackOverflow. Problem will be fixed in next build, however developers don't agree with you on the problem.

balpha might be right. I find the W3C's writing hard to understand and I can't vouch for Mozilla being right about its interpretation.

Anyway, it appears they fixed it, so mission accomplished.