User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.5) Gecko/20070713 Firefox/2.0.0.5 Build Identifier: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.8.1.5) Gecko/20070713 Firefox/2.0.0.5 (this issue occurs with a local file I was writing, I will attach it to this bug as soon as possible) I have a valid HTML4 markup and CSS2.1 style. (checked with W3C validator) The page has only one table, and this table has many pairs of TRs which should be displayed like this: +---------------------+---------------------+ | colspan=3 | rowspan=2 | +---------+-----+-----+ | | | | | | +---------+-----+-----+---------------------+ The first TR of each pair is called "first" and the second one is called "second" (by CSS classes). There are two CSS rules that trigger this bug: tr.first { border-top: 3px solid black; } tr.second { border-bottom: 3px solid black; } When any one (or both) of these rules is applied, then Firefox draws a horizontal line (1px) in middle of the TD with rowspan=2. The same happens if I change those two rules by these: tr.first td { border-top: 3px solid black; } tr.second td { border-bottom: 3px solid black; } If I remove these rules, then the bug is not triggered. Reproducible: Always Steps to Reproduce: 1.Open attached file. Actual Results: There is a horizontal line ("border"?) in middle of the TD with rowspan=2. Expected Results: There should be no horizontal line ("border"?) in middle of the TD with rowspan=2. There are some missing images on attached HTML file. That's intentional, the bug happens with or without those images in place. I've also tried to put: td[rowspan="2"] { background: yellow; } But then that line (that wrong border) was drawn on top of the yellow background.

File that triggers this rendering bug.

sounds like another way to reproduce https://bugzilla.mozilla.org/show_bug.cgi?id=367576

Yeah, I agree. Looks like a dupe of bug 367576.