Post your favorite add-ons or extensions for your web browser(s).
One of my personal favorites is called Disconnect. It increases your security while browsing and lowers bandwidth/increases the speed of which you load pages at the same time. It's a pretty great passive tool.

Another great one is HTTPS everywhere, which makes any websites with HTTPS available use it by default. (It makes webpages take slightly longer to load but is more secure than HTTP.)
Also if you're on Firefox (or a fork of Firefox like Pale Moon) you can also get HTTPS Finder which makes rules for websites that don't have HTTPS available.

Chrome - Adguard AdBlocker, Stylish, and Tampermonkey. I'm running a userscript called YouTube Center via Tampermonkey because Chrome doesn't allow you to enable 3rd party extensions outside of the Chrome Web Store.

Firefox - Adblock Edge, Stylish, and YouTube Center.

This list may expand in the future depending on my wants and needs.

Also, I think you should update the title to "Add-ons/Extensions/Userscripts".