Customizing default English dictionary in Firefox

1. Go to https://addons.mozilla.org/en-US/firefox/addon/us-english-dictionary and install English United States Dictionary
2. Go to about:config and toggle extensions.langpacks.signatures.required to false, and xpinstall.signatures.required to false.
   We will be editing the extension in-place and it cannot be signed by Mozilla
3. You need to close Firefox since we will be editing extension in use
4. Go to your Firefox profile directory (C:\Users\squeaky\AppData\Roaming\Mozilla\Firefox\Profiles\<id>\extensions), and
   find @unitedstatesenglishdictionary.xpi, open it with 7zip or other archiving program and edit dictionaries/en-US.dic.
   Be sure that after opening this file the file is replaced in the archive in-place. Alternatively you can unpack the whole .xpi
   and then pack it again.
   
   Each word is stored on a separate line terminated in UNIX \n line ending.
   While editing you need to add new words in __alphabetical__ order as this file is sorted.
   If you wanna remove words just search for them and delete whole lines.
   
 5. Once done reopen Firefox and you can test results

I cannot thank you enough for this work-around. I blog about my local government and have the bad habit of mistyping "public" as "pubic". After the Nth time, it ceases to be funny. Years ago, I manually edited the default FF dictionary to remove that word, but some FF update only "fixed" that for me and made any simple manual edit of the default dictionary impossible. It never even occurred to me to install ... well, the dictionary that should be installed by default. Then edit that. Beautiful. Worked like a charm. For now, at least, "pubic" appears on my screen with a delightful red underline. Again, thank you so much for figuring this out and taking the time to post it.