Maybe I’ve installed too many plugins? I have close to 20.
Edit: It was just an issue on Arch Linux.
No, I am 40 plugins all active and they have not changed my browser load time almost at all.
Make sure there are no other issues. If you are on Arch Linux, there is a problem with xdg-desktop-portal-gnome that if installed will slowdown loading of many programs.
Try starting firefox in safe mode. If the load time is still too long then it is not the plugins.