I use them all regularly. Here’s A-J of what’s currently turned on (I have a lot more installed but not turned on until I need them, like Full Page Screen Capture, or dotEPUB, which turns a webpage into an ebook):
1Password
Allow Right Click: Re-enable the possibility to use the context menu on sites that overrides it.
Allow Copy: Allow Copy will re-enable select, copy, paste and right click in any webpage, overriding site settings
BehindTheOverlay: One click to close any overlay on any website.
Decentraleyes: Protects you against tracking through “free”, centralized, content delivery.
DuckDuckGo: “Privacy, simplified. Protect your data as you search and browse. Permissions are to block hidden trackers lurking everywhere.”
EXIF Viewer: Quick access to EXIF data of any image you view
Fontanello: lets you select text, see font/style
Google Translate
Google Voice
Imagus: Enlarge thumbnails, and show images/videos from links with a mouse hover
Improve YouTube!
Just Read: customizable reader extension duplicating Safari Reader mode