Is this the spell check in Yahoo ? If so could be a issue there but you can add a Firefox Extension from here for a dictionary : https://addons.mozilla.org/en-GB/firefox/search/?q=dictionary&appver=&platform=windows or spell check here: https://addons.mozilla.org/en-GB/firefox/search/?q=spell+check&appver=&platform=windows

Note that there is a Firefox Update release later tonight or in the morning to ver 56.0.1

Please let us know if this solved your issue or if need further assistance.

Thanks for the help. Adding a dictionary made my spell checker work again. After the dictionary was added, the "Language" menu appears when right clicking text. My problem was that all the fixes I found said to right click on text and select a language, but that menu does not exist until a dictionary is added.