You should stay on WIndows 10 if possible. If you upgraded already from Windows 7 to Windows 10, then you are free to do a fresh install of Windows 10 to that computer in the future, and it will be activated.
- With regard to Problem #1, I'm sure there's an easy fix. It's definitely not an issue inherent to Windows 10 that I'm aware of. Keep doing research on the topic.
- With regard to Problem #2, have you attempted to clear Firefox's cache and restore the default settings? Have attempted to reinstall the program? Are you using the latest version of Firefox? Have you tried Google Chrome? Again, this doesn't appear to be a problem inherent to Windows 10 that I'm aware of.