From time to time it might be worth doing some on-demand scans with other products like Malwarebytes free and Hitman Pro (free) just to see if your active protection missed something. Note: You can scan with the free version of Hitman pro for as long as you wish, however if you use it to remove malware it will enter a 30 day trial period. If you want to keep it free, use it as the last scanner and if it finds something serious (besides tracking cookies) you could try removing the file yourself or ask for assistance.
If you find yourself wondering if a site is safe or not you could add Web of Trust, a Firefox plugin that will show you ratings for the sites you are about to visit. Note: ratings are generated by the community and sometimes non-malicious sites get a poor rating too.
LastPass is another Firefox plugin that I recommend. It helps you generate and store passwords is a secure manner.
In the end, no security is bullet proof. It is worth backing up your system partition to an external HDD using a drive imaging program like Paragon Backup and Recovery (Advanced) Free. Another great free option is Acronis True Image WD Edition (Free) but is only works if you have a Western Digital HDD.