I love the built-in dictionary in Firefox! However, one pet peeve of mine is the use of American spelling (or misspelling) for words like favour, colour, etc. How can I stop Firefox from marking these as spelling errors?

As with all things, there’s a hard way and an easy way to do this. Every time Firefox points out a mis-spelt word, it gives you the opportunity to add this to its dictionary. You could take it upon yourself to add each occurrence to your personal dictionary. This gives you ultimate flexibility as you can add technical terms and names that might not be in the in-built dictionary. However, this is also the hard way to get Firefox to do what you want.

The easy way to do this is to change Firefox’s dictionary from US English to British. This will immediately make these words available for you in their British spelling and save you lots of time. This is how you can do it

1. Browse Firefox’s list of available dictionaries here
2. Select the English (British) dictionary and install it

This will install the dictionary and ask you to restart Firefox.

You’re not quite finished yet. Firefox now has 2 languages available, but you haven’t specified that you want to use the British one yet. To do this, right-click on any text field, choose Languages and select “English / United Kingdom” from the list.

There you go, you can now use Firefox and ensure your words are all spelt correctly!