Show the issue. Here is the add-on I use to see the load time. https://addons.mozilla.org/en-US/firefox/addon/load-time/ Provide example sites that are slow for you. Who are you using for DNS? Try this tool to see if you can get a better provider. https://www.grc.com/files/DNSBench.exe

Absolutely all sites load several times slower. It seems that Firefox somehow slows down the speed of communication. One day, everything just started to slow down. Although I did not install or change anything in the system. This is not at all clear to me. Instead, Edge and Opera work without changes. So the problem is not in the provider, not in the network. Something happened with Firefox. Or the system (I have Windows 11) slows down the browser, is this possible?

Still no evidence of the issue.... Good luck.