When you type something in a form (text box) on a web site, Firefox automatically performs the spell check using an in built dictionary. When you type a wrong word, it underlines the mis-spelled word with a wavy red underline. You can right-click on such a word and use one of the suggestions as shown :
Often it happens that a word is not in the spell-check dictionary. You can always add that word by right clicking on that word and clicking Add to dictionary or you can manually edit the dictionary as shown below :
- Open Firefox.
- Type about:support in the location bar (where you type web site address).
- You would see a page with many sections. On the top, under the Application Basics section click on Open Containing Folder
- Close all the open Firefox windows.
- In the folder that opens in 3rd step, you would find a file persdict.dat. Open this file in Notepad or any other plain text editor of your choice. This file contains all the words that you added by right-clicking on a mis-spelled word and selecting Add to dictionary. You can manually remove or add new words to this file – one word per line. If this file does not exist, then simply create a file of this name in that folder.
- Save this file persdict.dat and start Firefox again. You would find that Firefox does not detect the added words as mis-spelled anymore.