The Best Overall Winner is Thumbnail Zoom Plus!
The Category Winners:
~ MOBILE (Firefox for Android) ~
Adds a translate button to the long-tap menu.
View and edit saved passwords on your phone, tablet or desktop.
~ MOBILE PORT (Firefox for Android) ~
Use your home button as you would in a desktop browser. Save from 1 to 4 links to open quickly with your new home button.
~ COMPLETE THEME (Desktop) ~
Smooth dark theme for Firefox.
~ UPDATED ADD-ON (Desktop) ~
Shows the full image when you hover over a thumbnail.