Vote for your favorite extension

[Hadden89]

Bulk Download Images (ZIG)

[TbGbe]

ImTranslator

[Zakro]

ContentBlockHelper

[ROTFL]

Eliminator Slajdów

[Stardust]

YouTube Plus (by Particle)

https://chrome.google.com/webstore/detail/youtube-plus/nkdalpbojfdilmiboaiedicdbigdabpb
also available for Firefox

[Ayespy]

The very boring Auto Copy which I use not because it auto-copies, but because it permits plain-text copy.

[Ayespy]

XMarks

[U.F.U.K]

Disconnect

[duarte.framos]

A TabMixPlus-alike

[duarte.framos]

Downloads Router (doesn't currently work in Vivaldi as far as I know, unfortunately)

[duarte.framos]

Image Viewer

[ugly]

FacebookBlocker

[ugly]

Facebook Redirect Fixer

[duarte.framos]

Scrollbar Anywhere
For me without this middle-mouse scrolling is utterly unusable

[pafflick]

Imagus

Shows large images (if available) when hovering over the small thumbnail.

[pafflick]

Viewhance

Adds features for the browser's default media viewer.

[U.F.U.K]

HTTPS Everywhere

[pafflick]

Google Translate

[pafflick]

Custom Style Script

It's not too handy for editing the code, but it allows injecting custom JavaScript and CSS on specified (or all) websites. I haven't found a better extension for this purpose (so far).

[pafflick]

User CSS

Even though i use Stylish on a daily basis, I find User CSS more convenient for editing the code "on the go", as the code editing field can be displayed right next to (or below) the page that I'm writing the code for...