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
Yes Yes 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