The plugin supports IE9+ on Windows and Safari 7+ on MacOS. You can view the detailed browser/os compatibility matrix here
Please note that with the release of the latest version of Safari, Safari 12, Apple has decided to remove support for third party NPAPI plugins in Safari. This means that third party plugins, including the Temasys WebRTC Plugin for Safari, will no longer work with the new version(s) of Apple Safari.
Other articles you may be interested in: End of Support for Temasys WebRTC Plugin on Safari 12 and onwards