When I try to drag a tab into its own window, it will open up by itself and then a moment later all the other tabs that were open appear next to it. This tends to only happen when I try to drag the first tab out into its own window, if I try to drag one that's in the middle of the group it works as normal. I've only noticed this happening in the last few weeks as I recently switched back from Chrome to Firefox after not using it for a while. OS X Mojave. I've uploaded a video of the bug here, showing that it only seems to affect the first tab: https://youtu.be/y3IoT6pbpl8 Thanks!