There is a new example project, only 4 KB as an mxb, published as server_sights.mxb in the miscellaneous downloads lists on the web site. Open this in the free Viewer or in 9.
This is a list of a couple of dozen locations that often pop up on Internet lists of interesting things that can be seen on Google Earth. The project includes a map with both Bing satellite and Google satellite layers since some sights are better seen on Bing than Google.
The .mxb link goes to symbol set in Firefox. You have to use a different browser to get the file.
In Firefox, right click the link and then click on "Save Link As" and it will download correctly.
Could that be something you've configured in Firefox? I've done a google search for firefox and .mxb and come up with nothing in firefox documentation. Magix bitmap format uses .mxb, but I haven't found anything online referencing that in Firefox. I don't use Firefox, but am curious what it does.
Goes directly to save or open the mxb in my version of Firefox 61.0.1 (64-bit)
Aussie Nature Shots