The page you are trying to view cannot be shown because it uses an invalid or unsupported form of compression.

I get this error from time to time when editing plain text files in Visual Studio. I tried correcting it by going to File, Save As, Save with Encoding (in the Save dropdown). This seemed to do the trick about 50% of the time. However, it would seem this was just coincidence. Latest findings suggest it is a Firefox cache problem. I tried the same URL in another browser and it worked. Fingers crossed this is a fix.