Firefox extension - website blocker

I want a program for the latest version of the Firefox browser that will block all websites from loading. I want to still be able to visit the URL, this is essential, but I want it to stop the actual page from loading (the HTML source code). In other words, whenever I visit a site I want to be staring at a blank white screen only. This will save me RAM and maximize my dialup connection so I can surf many more traffic exchanges at once. Secondly, this addon should have an allow list. Only sites that are added to this list should load. All others shouldn't. Third, I should be able to easily disable this extension. (Meaning, when it is off, I can browse as normal again, with all sites loading.) So let's recap the features: 1. Can visit URLs, but stops page from loading 2. Has an allow list 3. Can easily be disabled and activated again ------------------- If there is a similar program like this for Internet Explorer or you can make one, let me know. I could use that too. ;)