Double-clicking in Finder does not load files in MBM 8.6.8


New Member
I've been running MBM 8.6.8 on a Mac Pro, Early 2009, 2.66 GHz Quad-Core Intel Xeon, 20 GB of 1066 MHz DDR3, OS X 10.11.6. It never has loaded .mbm files if I double-click the file name in Finder. I can open the file if I use CMD-O. I've seen that this problem has occurred over the years in PCs. What can I do to get the files to open by double-clicking?