When using Outlook365 Online, about 2 or 3 weeks ago the spell checking stopped working. I checked to see if this was a Microsoft account issue and it is not because when I move to Chrome the spell check works. I am running Windows 11 Pro, it is fully up-dated. I have all of the latest Firefox updates as well. I have looked at several online help articles and have done all of the suggested fixes. The spell check is turned on in Firefox. I believe with a recent up-date of Firefox, as they come regularly it triggered the issue. When using other apps, and websites the spell check works fine just not with any 365 Online product. I do have Office 19 installed on my computer which I use off line.