Is your question about the normal user interface? If so, ePO 4.6 only supports IE and Firefox browsers. ePO 5.0 adds support for chrome and safari.
Most people developing scripts with the web API shouldn't be using a browser except for demos or experimenting.
So I've not had any luck getting firefox to open the portal, Is there a setting that needs changed in firefox running on a Mac?
Which versions of ePO and Firefox are you using and what are you seeing?