I have been having problems with Remote Front Panels not working anymore with IE as of the lastest MS security update. See here https://lavag.org/topic/19216-labview-ie-plugin-blocked-following-latest-win-7-update/
NI is still working on the issue, but based on my discussions it appears support for Remote Front Panels is bleeding a slow death. Here's how I would summarize the situation to date if you have the latest and greatest software versions and OS (Win7) updates:
Internet Explorer - Does not work, reason unknown (may be an ActiveX signing (Not Verified) or registration issue), being investigated (slowly) by NI
Chrome - DOES NOT WORK, npapi plugin no longer supported by Chrome and will not load in the latest version of Chrome
Firefox - Does not work by default, requires changing plugin settings to work.
Opera - Works currently, but plugin will not be supported in the future according to Opera
Regarding your situation with Firefox, I think you should be able to get it to work. My colleague was able to get Firefox working by changing some plug in settings. I am having trouble finding a link to the steps he took. This page looks old but may work:
http://digital.ni.com/public.nsf/allkb/CF91AE26198992A686257B79006959C0
bbean's post in IE crashes when opening remote panel was marked as the answer