>>> My Info: Win7_64, Nightly 49, 32bit, ID 20160526082509 STR_1: 1. Launch new Firefox profile 2. Swith Firefox window to normal (not maximized) mode 3. Open url "data:,red" in a new tab 4. Open url "data:,green" in a new normal window. Open url "data:,blue" in a new normal window 5. In the window with "data:,blue" click Australis menu -> Close Firefox 6. Launch Firefox profile from Step 1 STR_2: 1. Launch new Firefox profile 2. Maximize Firefox window 3. Open url "data:,red" in a new tab 4. Open url "data:,green" in a new normal window. Open url "data:,blue" in a new normal window 5. In the tab "data:,blue" click Australis menu -> Close Firefox 6. Launch Firefox profile from Step 1 AR: (read closely) In Step 4 the sequence of 3 Firefox windows on Windows Taskbar is: "red", then "green", then "blue". In Step 6: There're 8 stages 1) Firefox "red" window opens at the same place as "blue" window, and in the same mode (maximized/normal). The first tab shows "Connecting...". Actually, browser's trying to "connect" to about:home (see bug 1185158 that was intentionally ignored for a long time) 2) Tabs are created in that window 3) "red" window teleports to its position in normal (not maximized) mode 4) "red" window restores its real mode 5) 2nd FF window opens above other windows, becomes focused (either "green" or "blue") 6) 3rd FF window opens above other windows, becomes focused (either "green" or "blue") 7) "Connecting..." tab in the window from (5) closes, and a tab with normal url is created (see bug 1185158). During this stage, window from (5) is displayed above other windows 8) "Connecting..." tab in the window from (6) closes, and a tab with normal url is created (see bug 1185158). During this stage, window from (6) is displayed above other windows So, windows blink 6 times: (3), (4), (5), (6), (7), (8). "green" and "blue" windows restore their position and mode correctly, but they often switch places on Windows Taskbar. ER: All windows should be restored in their original positions on Windows Taskbar w/ minimal blinking Notes: 1) Explanation of ER (positions on Taskbar): After senseless removal of Panorama, I have to store tabs in several windows instead of tab groups, therefore I rely on windows positions in Taskbar (i.e. sequence of buttons in Windows Taskbar) My expectation is either 1.1 or some better ideas to restore Firefox windows positions in Taskbar 1.1) Firefox should first open necessary number of windows. When browser determines the sequence of opened windows, it should open each tab from the last session in correct window (1st, 2nd, etc) 2) Explanation of ER (blinking): At least one of 2.1, 2.2, 2.3, 2.4 or better ideas to recuce blinking 2.1) Firefox should first open the last focused window from the last session, focus it and place it above other windows. Then browser should open other tabs 2.2) When browser opens window, it should open it in the same place and same mode as in last session 2.3) When browser opens window, it shouldn't focus it and place above other windows (unless it's the tab that was the last focused in the last session) 2.4) When browser opens window, it should not focus it and place above other windows afterwards, when it opens tabs in that window (unless it's the tab that was the last focused in the last session) 3) Explanation of ER (further explanation) (1.1) in conjunction with (2.1) means either 3.1 or 3.2 if possible. Also, I'm sure that Firefox developers, who have better understanding, might know what _really_ can be done to fix this bug. 3.1) Firefox should open necessary number of windows [in Taskbar, but don't create the actual windows yet (normal windows, not buttons on Taskbar)]. Then, when browser determines the sequence of opened windows, it should open each tab from the last session in correct window (1st, 2nd, etc) 3.2) Firefox should open necessary number of windows [in minimized mode]. Then, when browser determines the sequence of opened windows, it should open each tab from the last session in correct window (1st, 2nd, etc) 4) It's possible for window to become focused and not placed above other windows. It's possible for window to become not focused and placed above other windows. This is not description of any bug, it's just my observations. On the contrary, this is what Firefox could probably use to recuce blinking. OS Windows 7 is obviously capable of doing this. I have STR for this, but don't know if it's possible to control this from Firefox side In particular, if last focused window was maximized, I should see only that window when I launch FF.

User Agent Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:53.0) Gecko/20100101 Firefox/53.0 Build ID 20170119030211 I am unable to reproduce the issue on Nightly (49.0a1, BuildID 20160526082509) and on the latest Nightly (53.0a1). After launching Firefox in Step 6 only one window is opened with about:home, if I click the "Restore Previous Session" button from the page the 3 windows are opened correctly and in the same position they were when I closed Firefox. Since the reporter's account is disabled and I cannot reproduce, I will mark the issue as Resolved-Incomplete. If anyone can still reproduce on the latest Firefox version, please feel free to reopen and provide more information.