hsgr-status-checker от Eleftherios Kosmas

This add-on adds an icon to the user's browser. In the background every 15 minutes the add-on checks hackerspace.gr's SpaceAPI to see if it's open for visitors. If hackerspace.gr is open the icon turns green. If the hackerspace states it is open a text badge is added to the icon to show how many people are in.

In case the icon is clicked it opens hackerspace.gr's main page in a popup