Fix Firefox opening IGB installer instead of downloading it on Linux

Situation: When testing IGB on Linux I ran into an issue when I tried to download the installer for IGB from BioViz.org. When I click on the Linux 64 bit link to download IGB the shell file is instead opened as a flat text file in the Firefox browser. And because it is a button instead of a link, there is no way to right-click and select "Download", which means that a Linux user on Firefox cannot easily download IGB.

Task: Fix it so that a Linux user with Firefox can download IGB from BioViz.org (early access and the download page). See this link for additional information.