Visual tab on one subsite is not functioning

I have one of my subsite users who does not have a working "visual" tab when in the post editor. The text tab is fine.

I can see the visual tab from my computer for this subsite fine.

I've done some searches on this problem, and it looks like it could be a caching problem with javascript files. One person recommended using the Google Libraries plugin as a solution.

But I wanted to ask the multisite experts for your opinion. I don't want to start adding plugins I don't need on my network. By the way, this plugin says it help relieve usage on the server because it uses Google's library instead of Wordpress. Is this true and a good idea.

Any other tricks for getting a functioning visual tab back besides just trying to clear the cached with F5?

Thanks, Joe.