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Where is Firefox's built-in en-US spellchecking dictionary located on Mac?

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Since Firefox does not allow for selecting multiple languages for spellcheck, as chromium-based browsers do, I want to create a hybrid dictionary file for both English and Spanish (duplicate built-in en-US dictionary file, rename it as en-es hybrid, and copy all entries of es-AR dictionary into it). However, first I have to find the built-in dictionary file. I've seen in another thread that on Windows, the file is apparently located in the Dictionaries folder in the Firefox folder in Program Files. Does anyone know where this file is located on Mac?

Thanks, David

Chosen solution

Hi cor-el, thanks again for your response. I ended up going with a simpler hack: I just pasted the full word list of my second language (Spanish) into the persdict.dat file. It seems to be working well so far.

Best, David

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Hi David.

In cuirrent releases the builtin dictionary is stored in the main omni.ja archive (resource://gre/). This archive is signed (has a META-INF folder) and thus it is impossible to modify this dictionary.

  • resource://gre/dictionaries/

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Hi cor-el,

Thanks for your reply.

I thought I had found a workaround with the English United States Dictionary add-on (https://addons.mozilla.org/en-US/firefox/addon/us-english-dictionary/), but after adding it to Firefox, I'm still not seeing the dictionary file in Profiles/.default/extensions.

es-AR@dictionaries.addons.mozilla.org.xpi is still the only dictionary file I see in that folder.

Best, David

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That English United States Dictionary extension would have this name:

  • @unitedstatesenglishdictionary.xpi

Firefox doesn't unpack the extension, so you would only see the xpi file and not the dictionary folder and the files in it. Extensions are signed, so you wouldn't be able to modify the dictionary.

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Chosen Solution

Hi cor-el, thanks again for your response. I ended up going with a simpler hack: I just pasted the full word list of my second language (Spanish) into the persdict.dat file. It seems to be working well so far.

Best, David

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Note that words added to persdict.dat aren't offered as possible suggestions, this merely prevents words from being flagged as misspelled.

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Right, thanks. I guess it's the best I'm going to do until the dev team is able to implement spell check for multiple dictionaries. I know this is something they're working on...but they've been working on it for years, so...I'm not waiting around for it.

If you have any other, more elegant, ideas of how to solve this problem, they would be welcomed.

Best, David

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You could create your own dictionary extension and get it signed.

Modified by cor-el

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Thanks, I'll look into this.

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