Notes about the MF1 file extension:
Incorrect file associations could be the result of underlying issues within your PC system. As such it is highly recommended to scan your PC for invalid registry entries, unused processes and other unfavourable system settings to identify slowdown issues.
The MF1 file type is primarily associated with 'NXI-deas' by Ford. Software originally developed by Ford in the 80's. This file type is legacy as Siemens ultimately owns NX now. They did away with I-deas and simply call it NX now and use a different file structure. MF1 files are your main model files and essentially contain the part files info.