I know how to add new words to Firefox dictionary, but how do I add them to the auto-suggest list when a word is misspelled?

I'm an electrical engineering student and many many terms associated with EE aren't in the dictionary, so I need to add them by hand. So when I type microcontroller, I don't get the red underline anymore, but when I type microcontrrler, I don't get microcontroller as a suggestion.


To add a word to Firefox's main dictionary, where it will also be used for both spelling checks and suggested edits, do this:

  1. Go to the Firefox installation directory. (Nominally: C:\Program Files\Mozilla Firefox\)

  2. From there, the dictionary is in the dictionaries subfolder.
    Select the file for the language you use. Typically: en-US.dic.

  3. Make a backup copy of the file -- en-US.dic.bak, etc.

  4. Edit the file with any text editor. To add words, just append them; you don't need to alphabetize.

    Notes about editing:

    1. One word per line.
    2. Words and flags are case-sensitive.

      1. If the entry is for Abigail, abigail will not be allowed.
      2. However, all-lowercase entries allow some capitalization. For example, if the entry is: "zonked" (no quotes):

        Word        Allowed?    Suggested?
        -------     --------    ----------
        zonked          y           na
        zonkedq         n         zonked
        Zonked          y           na
        ZONKED          y           na
        ZONKEDq         n         Zonked
        ZONked          n         Zonked

    3. You will notice a /, followed by uppercase letters, following some entries.   These are affix identifiers for the affixes stored in en-US.aff (or the appropriate file for your language).

      See this answer for more about how Firefox uses affixes.   See the Lingucomponent Project for even more gruesome detail.

      For now, you probably want to know the S and M affix-labels.

      1. S smartly handles most plural forms. For example, the entry microcontroller/S will allow and suggest "microcontroller" and "microcontrollers".

      2. M smartly handles most possessive forms. For example, the entry microcontroller/SM will allow and suggest "microcontroller's", in addition to the plural forms.

    4. While in the dictionary, delete the lines for whilst and withe, they have no business in there! (^_^)
    5. I like to keep the file in Unix format (as shipped). It saves a little memory -- and hopefully speed -- over PC format.

  5. Restart Firefox for the changes to take effect.

Right-click on the "misspelled" (the correctly spelled version) word, and select "Add to Dictionary." Or maybe you've done this, and this doesn't update the suggestion list as you desire?

  • It doesn't update the suggestion list.
    – AndrejaKo
    Jun 30 '11 at 23:59

On macOS, you can add your own words in

~/Library/Application Support/Firefox/Profiles/<profilename>.default/persdict.dat

Just add one word per line. To open the file you can use the finder, press Shift + Command + G and enter this path

~/Library/Application Support/Firefox/Profiles/

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.