HTTPS Everywhere is an extension created by EFF and the Tor Project which automatically switches thousands of sites from insecure "http" to secure "https".
Privacy Badger automatically learns to block invisible trackers. Instead of keeping lists of what to block, Privacy Badger learns by watching which domains appear to be tracking you as you browse the Web.
An easy to use ad blocker.
All recommendations on this list I either use myself, have used myself, or I know to be helpful to someone. For some items on this list, I may take part in affiliate programs; however, affiliate programs will never influence my recommendations.