>>> My Info: Win7_64, Nightly 51, 32bit, ID 20160913030425 (2016-09-13) STR_1: 1. Open new window, press Ctrl+T, press Ctrl+T 2. Drag and drop the 1st tab to make it the 2nd tab. Drag and drop that tab to make it 3rd tab. 3. Drag the tab from Step 2 by 5px to the left (w/o dropping) 4. Drag the tab from Step 2 to the left so that 2nd tab moved to the right AR: Step 3 - border between 1st tab and 2nd tab becomes more dark Step 4 - 1st tab has border at the right side. During 2nd tab transition I can see how border between 1st and 2nd tab splits into 2 borders ER: Step 3 - border between 1st tab and 2nd tab should be of normal color Step 4 - 1st tab shouldn't have border at the right side This is regression from bug 1157404. Regression range: > https://hg.mozilla.org/integration/autoland/pushloghtml?fromchange=7afc8055e8fbd09e5dd86da64e4a06cd98739821&tochange=fa8ec70570e65e1d21c4b301fbfd38ab568230da@ Mike Conley (:mconley) - PTO until Jan 3: It seems that this is a regresion caused by your change. Please have a look.

Mike, see this bug and bug 1353769. Any ideas what might be happening here?

(In reply to Ryan VanderMeulen [:RyanVM] from comment #2) > Mike, see this bug and bug 1353769. Any ideas what might be happening here? Not off the top of my head, no. :/