Try using Lunascape which is a browser that contains 3 rendering engines (Trident, Gecko, Webkit). I've used it for old sites where newer browsers fear to tread due to the cipher suites. Having a non-IE Trident browser is also convenient.
Use a powershell to set the Internet proxy to a nonexistent black hole. Eg, use Psexec (or Paexec) to remotely run a command like netsh winhttp set proxy 127.0.0.1:8080. Set it up as a scheduled task.
It may be due to the top name bar that remains visible as you scroll. Any way to test using the page code that does not include the stationary top name bar?
You can try wkHTMLtoPDF (or to image). The name says to pdf but it can save the output as a graphic as well. I did this for awhile when I needed to grab info from a PRTG monitoring page periodically for troubleshooting or historical reference.