This is a known bug in Firefox 4: [Bug 418975 - Soft hyphen not working in tables][1]. It has meanwhile been fixed, so a future update of Firefox probably resolves this.

Some background:

To avoid comments to mess up with the layout, [soft hyphens][2] are automatically inserted into comments after 81 characters without whitespace. For me, [that works well][3]:

![Comment with a long code fragment][4]

I have the same issue in Firefox 4.0.1 on Mac OS X, both for code fragments and for [normal text](http://meta.stackoverflow.com/questions/3122/formatting-sandbox/68144#68144) in comments. Still, despite the known bug: this does not *always* happen. [Sometimes](http://meta.stackoverflow.com/questions/88626/stackexchange-release-management) long comments wrap just fine, though [without visible hyphens](https://i.sstatic.net/B7cNF.png).

No problem in other browsers though.


  [1]: https://bugzilla.mozilla.org/show_bug.cgi?id=418975
  [2]: http://www.fileformat.info/info/unicode/char/ad/index.htm
  [3]: http://superuser.com/questions/256105/how-to-delete-a-folder-which-is-nested-quite-deep/256130#comment-265284
  [4]: https://i.sstatic.net/XuLJu.png