A totally miraculous add-on - uMatrix changed my life. It took a bit of learning, but quickly allowed me to dispense with several other add-ons, while giving me total control over what gets crammed down my browser's throat by the bloated monstrosities that pass for 'web sites' these days. Works terrifically well with Waterfox 56 on both Windows and Linux. (Sadly, this is looking like it may be the last version of Firefox I'll ever upgrade to. A big Bronx cheer to Mozilla...)
One suggestion: how about the ability to save multiple profiles for a site? (Right-click on the site name to select.) Very often I have a more relaxed secondary setup for making comments or accessing extra features. (On this site, for example, I had to allow cookies and extra scripts in order to post this review).