Some websites do not load in all my browsers
Do you experience this problem on other devices? From your question, it is clear that you have tried different browsers but you did not specify whether other devices can display these websites or not.
In order for website to displayed properly, the server (website's end) needs to set appropriate HTTP headers. Here is a sample of what those headers may look like.
When the browser gets malformed headers, it will not know what exactly to do with the received information so it will try its best. What will happen exactly will depend on the browser's implementation. As you have noticed, different browsers respond differently to malformed http headers.
As a general rule, there are several things you can do to troubleshoot:

https://downforeveryoneorjustme.com/ - if you do not have another device, you can use this service to test if the website is available or not
https://tools.keycdn.com/curl - or a similar tool - can be used to inspect headers; but the same can be achieved with Google Chrome - see this SO question