Please remove the second border in the header row of the applications pane in the in-content preferences, see screenshot.

It looks like an easy CSS fix. #typeColumn, #actionColumn { border-top: 0; } #typeColumn:-moz-locale-dir(ltr), #actionColumn:-moz-locale-dir(rtl) { border-left: 0; border-right: 0; } #actionColumn:-moz-locale-dir(ltr), #typeColumn:-moz-locale-dir(rtl) { border-right: 0; } Is this the correct approach?

That looks like a band-aid to the real problem. We should find out why the extra border exists in the first place and remove it so that we don't need to turn it off from some other place in our CSS. As a side note, while I agree that it would be nice to fix this bug, we should only have bugs that will legitimately stop us from shipping the in-content prefs marked as blocking bug 1014201.

Marking as NEW based on comment #2 ("We should find out why the extra border exists in the first place and remove it").

I think this bug can be closed since the new style has landed, there is no longer a double border.

Thanks Sören. Can you use mozregression to find which changeset fixed this? http://mozilla.github.io/mozregression/

No more inbounds to bisect Last good revision: a7d403088a16 First bad revision: f14dcd1c8c0b Pushlog: https://hg.mozilla.org/integration/mozilla-inbound/pushloghtml?fromchange=a7d403088a16&tochange=f14dcd1c8c0b (in this case the "first bad revision" is the first good revision). So I would say it was fixed by "bug 1087618 Part 1 : Introduce new tree style".

Verified fixed on Windows 7 64bit, Ubuntu 13.10 32bit and Mac OSX 10.9.5 using latest Nightly 39.0a1 (buildID: ) and latest Aurora 38.0a2 (buildID: 20150316004007).

latest Nightly 39.0a1 (buildID: 20150317030206)