It appears that Khaled was right. I had allowed mirc.exe to access all the necessary files and it was listed as a trusted program but Online Armor nevertheless blocked it from remotely controlling firefox.exe. This resulted in the right mouse click not working after trying to open a link.
Please accept my sincere apologies for the inconvenience. I just couldn't believe that anything could be wrong with the firewall settings since I had allowed mirc.exe to do what it wants to. I guess I'll have to once again start looking for a new, better firewall.
