XMLHttpRequest for JSON文件在Chrome中完美运行，但在Firefox中无法运行

I've narrowed my problem area down to the function below. It's part of a userscript I'm writing. It works perfectly in Chrome, but doesn't work at all in Firefox/Greasemonkey. I've tinkered with it all day and have hit a brick wall. The only thing that makes sense is if JSON.parse isn't working right, which would make sense since Chrome is known to handle JSON.parse somewhat differently... but I know the JSON is perfectly formed!I've narrowed my problem area down to the funct