Is it possible to replace Firefox's dictionary with a better one like MS Word's?

I really can't stand the dictionary that comes with Firefox. It doesn't catch tons of basic words (like shifter, for instance). I'm tired of having to constantly right-click -> add to dictionary.

Word has a much better dictionary, and conveniently also contains tons of the words I personally added (like names of characters as an example).

In a perfect world, I'd like to just copy the dictionary from Word to Firefox, but I'm not sure where to even find Word's dictionary, let alone if that would work or not.

So, is it possible to replace Firefox's dictionary with Word's? (or to point Firefox at Word's dictionary, or to get some kind of extension for Firefox that overrides it with Word's dictionary, or some other similar solution?)

Failing that, are there any third-party dictionaries that work better than Firefox's?

Edit: I am on Windows 10, FF version (whatever's latest - this is for multiple computers, so I can't check them all, but I'll update before attempting this).

Solution 1:

While I don't believe there is a way to access the entire MS Word dictionary, your Word custom dictionary is stored at this path:

%appdata%\Microsoft\UProof\CUSTOM.DIC¹

And your Firefox custom dictionary is stored here:

%appdata%\Mozilla\Firefox\Profiles\[unique string].[profile name]\persdict.dat¹

[unique string].[profile name] will be the unique identifier for your Firefox profile – there will likely only be one folder there so you should not need to worry about identifying your actual profile ID – the default will be named [unique string].default.

Both of these files are simple text files – just a list of words for the spell checker to ignore. You should be able to copy all your custom definitions from the Word dictionary to your Firefox one. Just make sure to format the definitions the same way as they are in the existing dictionary.

Hope this helps!
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¹ See What is “%AppData%”?

Solution 2:

Assuming you're referring to US English, Firefox currently uses the "normal"-sized SCOWL (And Friends) dictionary with some proper names added.

A word like "shifter" is only in the "large"-sized dictionary. This extension supposedly uses the large dictionary, but is no longer maintained.