Change firefox spell check default language

Question

Firefox has come to believe that my default spell check language should be Spanish. My global preferences have English selected:

Preferences->Content->Languages->English [en]

and on a page-by-page basis I'm able to reset the spell checker language via:

Right click->Languages->English (United States)

However, for newly opened pages or new sessions the default spell check language returns to Spanish. I found a workaround here: https://support.mozilla.org/en-US/questions/975459#answer-494574

Which suggested that installing a new dictionary would change the default. However, this issue has bugged me for so long that I would like to know if there is a more "correct" way to change the default spell check language.

Answer 1

Afaik, there is no UI for this. Instead you have to use about:config and set dictionary.spellchecker.

Also, Content > Languages has no bearing on spell checking. This effects what content you're given on multilingual websites.

Answer 2

If you only use system wide spell checking dictionaries (for example, the hunspell package provided by your Linux distribution) Firefox seems not be able to remember the default configuration (is this a bug?). You can fix this issue by having at least one dictionary installed as a Firefox plugin.