Unable to create new web links

I just updated to WP 3.6 earlier today. Now I am unable to create new web links on either posts or pages. The link icons are grayed out, so unable to click them! My existing links are still intact, I just can’t add new ones.
OK, I played around with it a little more, and it would work, then not work, then work, then not work…..
I use Firefox, version 22.0, and run Windows 7 Pro.