STR: 1. Load wiki.mozilla.org 2. Zoom in twice (with ctrl and "+") to get to 120% zoom level ACTUAL RESULTS: "Seams" appear at the right edges of the header label tabs for "Discussion" and "Page" I've got a minimized testcase, which I'll post shortly.

Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2a1pre) Gecko/20090622 Minefield/3.6a1pre

Here's a reduced testcase. Expected behavior is that no red pixels should be visible at any zoom level. The background image is 7px wide, and it's essentially offset 6px to the right of the span (due to the "padding-right: 6px" rule). So its leftmost pixel (which is red) should be covered by the span's background (which is green). However, in current mozilla-central, I see a vertical line of red pixels after "foo" at these zoom levels: 60% (partially red) 90% (partially red) 120% 200% 270% 280%

(BTW, the "Default Full Zoom Level" extension is handy for checking your current zoom level -- it displays it in the status bar)

I believe this is a existing bug - or something that came back.

You might be thinking of bug 477157 -- this bug manifests in a similar way to that one, but the underlying cause is probably different (since no CSS borders are involved here).

Regression-range good http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2007/10/2007-10-25-04-trunk/firefox-3.0a9pre.en-US.win32.zip bad http://ftp.mozilla.org/pub/mozilla.org/firefox/nightly/2007/10/2007-10-26-05-trunk/firefox-3.0a9pre.en-US.win32.zip http://bonsai.mozilla.org/cvsquery.cgi?treeid=default&module=all&branch=HEAD&branchtype=match&dir=&file=&filetype=match&who=&whotype=match&sortby=Date&hours=2&date=explicit&mindate=2007-10-24-01&maxdate=2007-10-26-01&cvsroot=%2Fcvsroot