Breaks websites in unexpected and unexplained ways (As in, as a developer, I can't explain it as simply a bug)

For example, a webpage that dynamically requests a JSON file from the server to populate a list, is suddenly replaced by the JSON file itself, with the direct URL of that JSON file in the address bar. This has nothing to do with an URL (i.e. a clickable link) needing to be 'cleared'. I didn't click anything and there is no link to speak of.