Comment 3 for bug 991895

I was discussing this with someone yesterday, and I suspect it might be an interaction between Webkit and the graphics system. Are you using Intel graphics hardware?

Have you noticed any other behaviour like this, anywhere? (Especially in the help browser or in browsers using native WebkitGtk, like Epiphany or Midori).

While the slideshow can work around this, it's unlikely a bug in the slideshow: all it does is change the opacity of elements, which Webkit then draws.