I've had this problem for quite a while now. When scrolling through slideshows on any site linked to my home page (https://att.yahoo.com/), selecting the next frame nearly always results in skipping over it to the following frame; e.g., if I'm on the first frame of the slideshow, clicking the forward arrow results in the second frame being momentarily displayed, then being replaced by the third frame. Proceeding backwards has the same problem. Viewing the same page with Internet Explorer results in proper slideshow behavior. I'm running Windows 8.1 x64 Enterprise with all current updates and Firefox v35.0.1.