Hi rjtc, when you close the computer, is MacOS shutting down all the way, or is it going into sleep/suspension? Usually you can tell when you open it again, because a full startup takes much longer than resuming from suspension or waking from sleep. If it's a full shutdown, I suggest quitting Firefox before closing your computer. You can use either: * "3-bar" menu button > power symbol (lower right corner of the menu) * (menu bar) Firefox > Quit If it happens when you resume from sleep, are you getting the Mozilla Crash Reporter form? In that case, your Firefox may have logged some data that would help track down the cause of the problem. You can submit that data to Mozilla and share it with forum volunteers to see whether it points to the solution. Please check the support article "[[Firefox crashes - asking for support]]" for steps to get those crash report IDs from the about:crashes page, and then post some of the recent ones here.