I am using Firefox 85.0.2 (64-bit) on a Macbook running OS X 10.13.6. This problem has been afflicting me for six months or so. On certain websites that open a new page in a new window, the new window instantly enters what I would describe as a "resizing loop": the window starts small and immediately maximizes. Each time it fills the screen, though, it immediately shrinks back down and starts again. This looping behavior continues endlessly, until I kill Firefox or somehow manage to get the malfunctioning window to close. On my employer's webmail, for instance, I'm not able to compose a new message, because it tries to open a new window and gets stuck. The resizing is very fast and very incessant, fast enough to induce nausea in the unsuspecting user. Can anyone offer any suggestions?