91.0.1 (64-Bit) regression, works in 78.13.0 (32-bit)

STR

• Show main menu bar
• drag a TB tab to another position

Actual result (see screenshot)

• drop marker shows in menu bar

Expected

• drop marker should show in tab bar

Note that TB is not using the latest FF tab layout where tabs are irritatingly presented as buttons which are disconnected from their content.

Regression from https://hg.mozilla.org/comm-central/rev/4a6f152a44d9b97103710a75f9624badc7f50531

I don't see this on linux. Is this on windows, because I think the problem might be that the tabs element is missing the position: relative rule https://searchfox.org/mozilla-central/rev/d3683dbb252506400c71256ef3994cdbdfb71ada/toolkit/themes/windows/global/tabbox.css

Can you confirm this using the toolbox rules tab? The drop icon is positioned absolutely with respect to the nearest positioned parent, which should be the <tabs> element, but without the rule it would probably be the window itself.

Note that linux and osx have these rules:

https://searchfox.org/mozilla-central/rev/d3683dbb252506400c71256ef3994cdbdfb71ada/toolkit/themes/osx/global/tabbox.css#28
https://searchfox.org/mozilla-central/rev/d3683dbb252506400c71256ef3994cdbdfb71ada/toolkit/themes/linux/global/tabbox.css#14

It might make sense to share a tabbox.css between platforms.

The problem is that Windows is missing this https://searchfox.org/mozilla-central/rev/d3683dbb252506400c71256ef3994cdbdfb71ada/toolkit/themes/linux/global/tabbox.css#15. Mac doesn't matter as the menu is in the screen title bar.

We could also add this to our windows tabmail.css. A simple

#tabmail-tabs {
  position: relative;
}

in it should fix this.

(In reply to Richard Marti (:Paenglab) from comment #3)

The problem is that Windows is missing this https://searchfox.org/mozilla-central/rev/d3683dbb252506400c71256ef3994cdbdfb71ada/toolkit/themes/linux/global/tabbox.css#15. Mac doesn't matter as the menu is in the screen title bar.

We could also add this to our windows tabmail.css. A simple

#tabmail-tabs {
  position: relative;
}

in it should fix this.

Yeah, I didn't realise that tabbox.css is in mozilla-central. This makes sense for us.