Yea, it was only that way for a second or two. I don't know if its related but I've also lost my spell check on this site around the same time. Marcel offered advice but in the end still no spell check.
Please check if the option hasn't been switched off.
Click the icon in the top right corner of the Firefox ( three black horizontal lines ) then go to ... Options -> Advanced -> tab General -> and mark the option Check my spelling as I type if unmarked.
Then close the Preferences page.
Also click on the field of the Reply window with the Right Mouse Button. Check if in the pop up menu is the Check Spelling option marked. If is not just click the option. It will switch it on.
Glad to hear that. The issue you reported in the first post here might have been the reason. Perhaps either the Win or Firefox updates set a couple of settings default and disconnected the dictionary.
All good in Google search but I test drove this in a few other sites and the plurals are listed as errors as well. Something weird just happened. The first plural and the word "happened" had the red squiggle under it but as I kept typing, the squiggle went away. Weird!!!
Have you switched on the option "Search for text when you start typing" of the Firefox we were talking about in the post #8 and #9? Maybe you need to disable it now.