As mentioned many times before (I should add this to the FAQ part), it depends on the website, this observation is not global. Many servers provide filename extensions one way or another, but e.g. twitter doesn't in any way (because websites don't need to) and my addon can't just take a wild guess as it. There will be an extension if the extension is communicated by the server as per standards. What a blown-out-of-proportion thing to give a permanent 1 star for anyway, as if that's all there is to it and as if it's any addon's fault a server decides not to expose extensions. Stupid "reviews" - more like baseless whines - like this are why I'm done developing for the public anyway.