User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:58.0) Gecko/20100101 Firefox/58.0 Build ID: 20180207210535 Steps to reproduce: When I have multiple Firefox (FF) windows open, each with 3+ tabs, overlaping each other, on the same desktop, if I attempt to drag a tab from FF window #1 to #2, the alt-tab switching is prevented. Actual results: Alt-tab task switching cannot be done until the drag process completes. This means repeated attempts to alt-tab do nothing. Expected results: Start drag even, alt-tab to another firefox window starts and completes, the drag event is still active and tab can be dropped into the tab strip of the target firefox window. This is the default behavior on Windows.

The issue was discovered on Manjaro Linux v17.1.5. The following output comes from "screenfect -n" in a terminal: OS: Manjaro 17.1.5 Hakoila Kernel: x86_64 Linux 4.14.20-2-MANJARO Uptime: 12h 46m Packages: 1069 Shell: bash 4.4.18 Resolution: 1920x1080 DE: KDE 5.43.0 / Plasma 5.12.1 WM: KWin WM Theme: Breath GTK Theme: Breath [GTK2/3] Icon Theme: maia Font: Noto Sans Regular CPU: AMD Ryzen 7 1700X Eight-Core @ 16x 3.8GHz [39.8°C] GPU: GeForce GTX 1060 6GB RAM: 3488MiB / 16035MiB The following URL is to a thread I created in the official Manjaro forums: https://forum.manjaro.org/t/dragging-firefox-tabs-v58-0-2-prevents-alt-tab-switching-in-kde/41213 I do not think that the erroneous behavior in Firefox is a KDE specific issue because the Dolphin file manager in KDE exhibits the default windows style behavior described in the "Expected Results" section of the bug report.

User Agent: Mozilla/5.0 (X11; Linux x86_64; rv:58.0) Gecko/20100101 Firefox/57.0 I have tested this issue on Arch Linux 4.12 x64 with the latest Firefox release (58.0.2) and the latest Nightly (60.0a1-20180301024724) and managed to reproduce the issue. When having multiple Firefox windows open, each with 3+ tabs, overlapping each other, on the same desktop, if attempting to drag a tab from Firefox window #1 to #2, the alt-tab switching is prevented.

Duplicate of https://bugzilla.mozilla.org/show_bug.cgi?id=1276449?