Since I found the rant against the Pando Media Booster in the other answer a bit inadequate, I've done some research.
First, it's clear what Pando Media Booster is and it is also clear that some (free to play?) Games use it to download the installer: For example, the free to play DDO game will tell you very clearly that it is going to use PMB to download the 3-4GB of installer data.
It does not tell you that it will install a browser plugin however, and there really doesn't seem to be any good info what the plugin actually is supposed to do.
But let's take a peek at the plugin database of Firefox, located at (Win7) C:UsersUSERNAMEAppDataRoamingMozillaFirefoxProfilesprofilename.defaultpluginreg.dat: It's a rather messy textfile, but some info is found easily enough: