It's a Developer extension. Clicking on Switch Env icon, will open the same URL but in the development environment that is configured.
First, you have to configure in the option page the 'switch' for an specific URL and his development URL. For example: twitter.com to http://localhost:8080/some-path
So, when you're in http://twitter.com/matiascarranza, click on the icon and a new tab is opened with the url http://localhost:8080/some-path/matiascarranza.
Also, you can change the "localhost" to an especific URL or domain, such as 192.0.0.1 or dev.example.com
The port and path options are optional.
Extore is a team of professionals who are passionate about creating extensions for web browsers. This devotion also gives us opportunity to appreciate work of other people. We get inspired by useful, open source extensions made by developers all over the world. Our strong belief is that one should share helpful add-ons with others. That’s why we’d like to present you our ever-growing list of favourite extensions that have inspired us. Moreover, as you probably have already learned, sometimes struggling for the best brings an end to the good. Talking about add-ons it often turns out that an upgrade is worse then previous version. Also it can become really tricky to get back to the beloved version of your favourite extension. That’s why we’re going to make not only the latest, but all versions of our favourite (and we hope yours too) add-ons available for download. No more compromises, just stick to the version you really like!