Imagus for Firefox

Imagus for Firefox is a browser extension that aims to replace Firefox’s default viewer with a more customizable and feature-rich media handler. It uses its own inner engine for the task, without relying on third-party services or anything on this sort (as opposed to similar extensions).

Enhance your browser's media handling capabilities

Imagus was created to benefit users whose needs go a little beyond the capabilities of the built-in photo viewer of Firefox and SeaMonkey (yes, it is compatible with this one as well), offering extended zoom and hover functions, on top of which there are possibilities to export images to various sharing services.
If Firefox isn’t your bowser of choice, the extension is also available for other popular browsers such as Opera, Chrome and Safari, with the observation that the functionality of the add-on inside the navigators is equivalent.
In order to accommodate it inside the browser, simply drag and drop it on an open window and give it permission to install. There’s no need to restart Firefox in order for the changes to take effect, so there’s the first advantage of working with it.

Fully customizable Firefox extension

More upsides will become obvious once you start experimenting with its features. But before you do, it is recommended that you navigate to the Options section in order to tailor its behavior to your needs.
This section is home to a variety of preferences that concern the viewer itself (sizing mode, resolution, background, image border, zoom and the possibility to configure shortcuts for various actions), the hover zoom function that will arrange for images to be instantly magnified when you hover the mouse over them, as well as the Tools section, where hotkeys for zoom and image sharing can be configured.
There’s also the Sieve feature that allows to define a set of rules based on regular expressions for operations with larger images.

View photos, videos and GIF animations in a much more convenient manner

All in all, Imagus for Firefox comes across as a better and more user-oriented media viewer that provides a rich array of customizations, which make the photo and video viewing experience simply more enjoyable.