Globally, the back button on my MX Master S3 is set to "Back". I have added a profile for the application Irfanview. For this app, I set the back button to the shortcut Ctrl+H.

At some point, Firefox back button will stop working. Instead, it will show the browsing history instead of going back to the previous page. In Firefox, Ctrl+H is the shortcut for showing the history.

However, I have set the Ctrl+H only for the Irfanview application, not globally! This is an annoying bug, the only fix is to completely reinstall Logi Options+ and setting up all applications profiles again. It will work for a while, until it again breaks the Firefox back button. Rinse and repeat...