Why don't websites work on certain browsers?

Hi everyone, I have the problem that different pages only work on certain browsers, which is of course annoying because I would rather only use one.

Examples: The Media Markt website doesn't work for me in Chrome, or only works very poorly. I can't log in (it tells me to check my internet connection), and articles only load occasionally. Everything works fine in FireFox. However, a regular Google search doesn't work in FireFox. It just loads endlessly, without any results. After a few minutes and several restarts, it works again.
Those were two examples of what the problem looks like. I constantly have to switch between browsers or use them simultaneously.

Otherwise: Both browsers are in normal mode, meaning no plugins, etc. I also reset both and deleted all data –> No help.

Maybe someone has an idea.

Thanks in advance and best regards