Ah, ok Ii took a look. This isn't a FoldingText bug per se, it's a feature. I believe it's the default security setting for OS X apps to to prevent insecure connections. So, in this case, imgr provides both links and the https protocol will work, as you know. There is nothing appropriate I could implement to bypass this since it's there for a reason. I would simply use the secure link!
I have updated the plugin to supported local files as well. Thanks