My configuration (which matches OS X version, Safari version, and SlingBox 350, but differs by my computer having SlingPlayer Plugin 18.104.22.1680) works correctly.
1) Are you sure you're not on SlingPlayer Plugin for OS X 22.214.171.1240? I doubt you'd be able to stream if you weren't. See Help -> Installed Plug-ins... in Safari.
2) Is it possible the video zoom/aspect settings on your home cable/satellite receiver have been changed?
3) Is it possible to have your home cable/satellite receiver change what resolution it's outputting? e.g. maybe this is specific to 1080i versus 720p. (note my DirecTV HR24 receiver is outputting 1080i over component)
Thank you for the feedback.
I have now uploaded 126.96.36.1990 and the problem remains the same.
I don't think it is the source as my two sources are in different countries, with different sling boxes (350 and Pro). I know that the settings on the cable/satellite receivers have not changed, nor the connections. The only item to have changed recently is the SlingPlayer Plugin.
The 350 is fed by component from a Comcast Box which is simultaneously feeding 1080i to the television.
The Pro box is fed with s-video and is of course lower resolution, although Standard Resolution is higher in Europe (625). However the picture from the Pro has also deteriorated since the SlingPlayer update.