Posting this as it might help someone. I have used firefox for years and love the sync facility for passwords. Recently firefox became very slow and sometimes even froze. Went looking for a solution on the intenet and tried everything to no avail. Eventually uninstalled and removed every trace of firefox. Renistalled and everything was ok for a short while. Soon back being incredible slow. Chrome seemed to work much better and was acceptable. However while doing a test on intenet speed I got an error message from the site saying a firewall maybe preventing access. Made me think. No firewall problems on my router as my other computer with firefox on the same router was fine. Windows defender switched off. I then remebered I accidentally ended up with real time protection from malwarebites premium trial . I did not ask fot it. I switched real time protection malwarebites premium features off and rebooted computer . Everything fine since then. Firefox super fast and chrome a lot faster too. Hope this helps someone