I usually want spellchecks "English (United kingdom, large)" and "German (Germany)" active. Every few days to weeks it changes to a (single) random other language instead, like "German (Luxembourg)". Posts I've found elsewhere suggest changing display language (which should be unrelated and is already set to UK English), uninstalling all other dictionaries system-wide (which should not be necessary and is not acceptable), reinstalling Firefox entirely (but that's for cases where the correct dictionary was never selectable, I can select it, it just doesn't stay for long) or issues with syncing with other devices (but I don't change that setting on other devices, either). How do I stop spellcheck from changing and why does this even happen?