During further investigation, I discovered that the issue related to the editing of content in the WYSIWYG field and Firefox has been reported to the concerned team, already.
I don't have a time estimate to share at this time, but, I'll keep you updated through this ticket.
still having this issue with firefox browser. I figured out that in mode "Visual" it shows CSS aria hidden "true".
this is definitively an issue by firefox. and it's annoying. can't edit anymore.
We expect this issue must be resolved before the Visual tab is working correctly, and I'll let you know as I receive more information about this problem.