How stable is it when you're just getting webpages with normal HTTP?
It could actually be a problem with your wiring... The ESP8266 draws quite a lot of power when it's going, and if the connections aren't good it can cause a lot of unreliablility, and I guess potentially the corruption you are seeing.
Espruino is a JavaScript interpreter for low-power Microcontrollers. This site is both a support community for Espruino and a place to share what you are working on.
How stable is it when you're just getting webpages with normal HTTP?
It could actually be a problem with your wiring... The ESP8266 draws quite a lot of power when it's going, and if the connections aren't good it can cause a lot of unreliablility, and I guess potentially the corruption you are seeing.