Windows 8.1
Firefox 43
It seems that since the update to Firefox 43, the google voice and video plugin (for hangouts calls for instance) doesn't load in Firefox Portable even though it loads just fine in the local installation of Firefox. Even after reinstalling the plugin multiple times, the results are the same.
Are there some changes that we need to load this plugin now?
You have to set Firefox to run in 32-bit mode using AlwaysUse32Bit:
https://portableapps.com/support/firefox_portable#32and64
Firefox Portable now combines 32-bit and 64-bit. When 64-bit is running only the Flash plugin is allowed. The same will be true of 32-bit later in 2016. At that point no plugins other than Flash will be allowed in Firefox, same as it is with Chrome, Microsoft Edge, etc.
Sometimes, the impossible can become possible, if you're awesome!
Thanks John! All is well once again.
As a sidenote, the AlwaysUse32Bit option is currently missing from the source ini file.