Hello,
Zoiper WEB requires NPAPI support. Unfortunately most browsers have dropped the support for NPAPI plug-ins. You can still use Internet Explorer, as Zoiper WEB also has ActiveX version, or older version of Firefox/Chrome.
I think that the Maxthon browser has kept the NPAPI/ ActiveX support till recently and maybe they still do, however I can't say for sure, I can only suggest that you check them.
