From Bugzilla Helper: User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.0; en-US; rv:0.9.5) Gecko/20011011 BuildID: 2001101117 user/pass for the above site is studio/dev <hr> elements overlap floated box objects. Reproducible: Always Steps to Reproduce: You can create the effect easily on a new page. Create a Div object and use CSS to float it right. then create some text that flows around the div. In that text create a horizontal rule such that the rule should be beside the box. Instead of stoping when it reaches the div, it runs right across the top of it. Expected Results: stop the <hr> at the same place the text stops at.

Duplicate of "[FLOAT] <hr> is drawn over complete page in standards mode" In quirks mode we do the backwards-compatible behavior. In standards mode <hr> is a block element and acts like one. *** This bug has been marked as a duplicate of 84887 ***

This should probably be considered a bug in the specs, not a bug in Mozilla. The solution for webmasters is to redefine hr to be an inline element: hr { display : inline } ... whenever a strct DTD is used.