User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:92.0) Gecko/20100101 Firefox/92.0
Steps to reproduce:
My OS is Windows 10 (64 bit, 20H2). At the last update of Firefox I noticed that when I start it initially, and also when I open each new window, the regional language settings are not remembered, and the language automatically switches to English. Through trial and error, I found that when I entered in "Customise Toolbar..." (even without changing anything), the browser "remembers" the regional settings and switches to them again (I made a short video where you can see this). I wonder if anyone else has the same problem ...
(see the attached video)