You're welcome, Ramona. Yes, hope this is what he wants.
I always read about what other people have to say before I try any extensions. This particular one does not have very favourable reviews. The one I like most is the clock.
I also make sure I have a good clean image backup before I install any extensions because some of them can't be uninstalled. Another way to remove extensions would be an uninstall of Mozilla, remove whatever files related to the extensions in the Profile folders and reinstall Mozilla.