Firefox is spell checking using the wrong language. I'm using the latest version of Firefox (80.0) on Linux Mint 20 Cinnamon 4.6.7 Originally after installing Linux on the computer, Firefox which came pre-installed was correctly showing English (United Kingdom) on the options screen and spell checking the same. Test with colour color <- here it is spell checking using American English. On other pages it tests using Canadian English or South African English! How do I fix this problem so it spell checks using the language I've told it to spell check using, i.e. British English without it keep picking a different one at random?