Do you use an extension to manage your tabs? I haven't experienced this on stock Firefox, but a few years ago I had Tree Style Tab installed and it would occasionally do this.
(I now use Sidebery.)
(I now use Sidebery.)
Currently, the problem might be gone, I will try that out. Thanks for your answer!
Edit: I also don't have these stability issues, but I did have issues with my suspend mode on that laptop, no matter the os (win/ubuntu)