If you see a message when opening the browser extension that says Unable to establish a connection it means that the version of the app you have installed is too old to be compatible with the browser extension.
You should be using at least build 122 of the app.
Or it could mean that your installation has been corrupted; the extension communicates with the app using a helper executable called sos-native-bridge. If that executable is not found in the correct location the extension and the app won't be able to communicate.
There are also native manifest files that need to be present so the browser can locate the executable, the location of these files varies by platform and browser.
Our installers add the helper executable and manifest files so the solution is to download and then install the latest version of the app.