@ppc910 - This appears like it might be an issue with previous versions of Firefox. Does your operating system allow you to update Firefox to a later version (current version is 31.0)? Also, can you give Chrome a try? I'd like to see if this is isolated to Firefox or something larger.
@v0yelle - When you say you're "unable to set new featured images," can you explain a bit more about what you mean? Is the "Featured Image" module missing from your Edit Page screen? If so, can you check under "Screen Options" at the top of your Edit Page screen?
@barbaramolony - Can you let me know a bit more about what error message you receive when you try to upload? What happens when you drag and drop an image or select it through the Select Files button?