The best browser to use is Internet explorer.
This is what I absolutely recommending but Firefox is supported by below mentioned document.
Supported Platforms, Environments, and Operating Systems for McAfee products
Supported Platforms, Environments, and Operating Systems for ePolicy Orchestrator
and 1 thing more is check your SSL in Firefox and insert the ePO certificate manually in Firefox.
Internet browser versions
|Browser||ePO 4.6||ePO 5.0||ePO 5.1|
|Safari 6.0 and later (on Mac OS X)||No||Yes||Yes|
|Chrome 17 and later||No||Yes||Yes|
|Internet Explorer 9.0 and later|
|Internet Explorer 8.0||Yes||Yes||Yes|
|Internet Explorer 7.0||Yes||No||No|
|Mozilla Firefox 10.0 and later|
It should not give any issue, try to disable popups option and see if its fix the issue