Extensions or addons

✅ Yeah, I won't post it in the comments.

ESGST Firefox addon, Secret Sniffer and Rachart Enhancer userscripts.

I use these ones (for Opera browser):

1. Disable HTML5 Autoplay - it's pausing all these pop-up windowed videos and other stuff that starts automatically
2. Disable Youtube™ HTML5 Player - like the previous one but for YT.
3. Mate Translate – translator, dictionary.
4. Notifier for Gmail™ - you no need to log in to your mail, it's shows you when you receive a new mail.
5. Opera Ad Blocker - build-in Opera ad blocker
6. uBlock Origin - better than the previous one and most of the sites doesn't detect it.
7. Select like a Boss - let you select most of the texts
8. Steam Inventory Helper
9. PhotoTracker Lite - something like "search by the image" from Chrome
10. Pure URL - makes some links shorter
11. Tampermonkey
12. Video DownloadHelper - let you download videos from sites (I usually use it to download some episodes from tv series)
13. Zoom for Opera
14. Install Chrome extensions - let you install extensions from Chrome Web Store.

I have a few userscripts that I made myself, although I don't think I put any new ones up on the Internet since userscripts.org closed down. I'll see if I can change that.