Some sites have set a Content Security Policy and therefore ASLint and any other resources not defined in that Content Security Policy will not be loaded. The easiest way to check this is to open the browser console and check what's in there. See examples from a few browsers:
Google Chrome (53.0.2785.143 (64-bit), OS X): Refused to load the script '//18.217.221.135/api/aslint/loader/loader.js' because it violates the following Content Security Policy directive; [...]
Firefox (49.0.1, OS X): Content Security Policy: The page’s settings blocked the loading of a resource at //18.217.221.135/api/aslint/loader/loader.js [...]
Safari (10.0 (12602.1.50.0.10), OS X): Refused to load //18.217.221.135/api/aslint/loader/loader.js because it does not appear in the script-src directive of the Content Security Policy.