There are many posts here about Firefox being "slow". I don't find that, most of the time, operations in recent Firefox are slow, however, EXITING Firefox in very recent versions (and particularly with v158 including v158.0.1) can be quite slow. (This is on Windows 11, 64-bit, 25H2, 26H2).
I routinely use Firefox only for a small number of fixed, long-running tabs - a Google Translate, a couple of other linguistic tools, and WhatsApp Web (which is almost certainly the instigator).
When I click to exit Firefox, I can sit staring at Task Manager as the Firefox processes gradually drop off until the program has fully existed, taking as much as a full minute+ (on a 4-core/8-thread 3.8GHz Xeon CPU with 32G RAM, all PCIe NVMe storage, not heavily loaded machine; other than that it is managed by Microsoft Intune and does have Microsoft's MsSense and MsMpEng security tasks operating).
