User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0.1) Gecko/20100101 Firefox/4.0.1 Build Identifier: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:2.0.1) Gecko/20100101 Firefox/4.0.1 In older version of firefox, this tags used to work as expected. with the newer version: <dd> tag that follows the 'Previous Topic:' section shown at the wrong section. Reproducible: Always Actual Results: "Busted" link is located at unexpected location on the page. Expected Results: "Busted" link should be located next to "Previous Topic:" on the page.

Reproduced, somewhat. For me "Busted" is indeed located next to "Previous Topic:", but instead "Topic pages:" and "1" has been split. Mozilla/5.0 (X11; Linux x86_64; rv:2.0.1) Gecko/20100101 Firefox/4.0.1 Mozilla/5.0 (X11; Linux x86_64; rv:6.0a1) Gecko/20110519 Firefox/6.0a1 WFM: Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.2.17) Gecko/20110420 Firefox/3.6.17 Regression range: Last good nightly: 2010-08-05 First bad nightly: 2010-08-06 Pushlog: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=bbefb7bcb41e&tochange=26ee1b556bd9

The W3C Markup Validation Service reports 44 errors and 11 warnings. http://validator.w3.org/check?uri=http%3A%2F%2Fcalifornia.adultsearch.com%2Fforum%2Fviewtopic%3Ftopic_id%3D11868%26p%3D11963%2311963&charset=%28detect+automatically%29&doctype=Inline&group=0 The The W3C CSS Validation Service reports 97 errors. http://jigsaw.w3.org/css-validator/validator?uri=http%3A%2F%2Fcalifornia.adultsearch.com%2Fforum%2Fviewtopic%3Ftopic_id%3D11868%26p%3D11963%2311963&profile=css21&usermedium=all&warning=1&vextwarning=&lang=en

I dont think any of those validation errors have anything to do with this bug. Firefox 3.x version shows the css as expected, this happened version starting from 4.x

The first bad revision is: changeset: 48999:66c78df18e50 user: L. David Baron <dbaron@dbaron.org> date: Thu Aug 05 21:59:20 2010 -0700 summary: Pass correct *remaining* height to float manager, rather than the whole height of the content area. (Bug 563584, patch 22) r=roc

Hmm. So this page is using a negative top margin to pull the floats up. But it's using a "-2em" margin, and there's no good reason that would be enough to line the float up exactly with the <dd> to its left (even though the latter has line-height forced to 2em. So as far as I can tell, the float just doesn't fit and so moves to the next column....

A minimal testcase would be a good idea.

I've written a minimal testcase that mimics the layout on the site and shows the layout error with Nightly 2010-08-06 and on.

Mozilla/5.0 (Windows NT 5.1; rv:6.0a1) Gecko/20110503 Firefox/6.0a1 Considering the added testcase - setting resolution to New.

Regression window: Last good: Mozilla/5.0 (Windows NT 5.1; rv:2.0b4pre) Gecko/20100805 Minefield/4.0b4pre http://hg.mozilla.org/mozilla-central/rev/bbefb7bcb41e First bad: Mozilla/5.0 (Windows NT 5.1; rv:2.0b4pre) Gecko/20100806 Minefield/4.0b4pre http://hg.mozilla.org/mozilla-central/rev/26ee1b556bd9 Pushlog: http://hg.mozilla.org/mozilla-central/pushloghtml?fromchange=bbefb7bcb41e&tochange=26ee1b556bd9

(In reply to comment #9) > Regression window: ... And changeset 66c78df18e50 has already been tracked down in comment 4. :-)

And thank you for that :)

My guess is that either: * the new behavior is correct, or * the issue is that we no longer fit a 0-height (or negative height) float in a 0-height space

I can reproduce this issue on 49.0a1 Windows 8.1 x64.