Try download in another browser if MX is having issues. Although works fine here.
Also check what version you already have installed: http://www.adobe.com/software/flash/about/
Been playing around with creating an auto updater seeing as fiddling around with files isn't the most user friendly thing for most people. You can try the file attached.
It will detect your MX and installed flash version, update Flash if it's not the most recent, and copy over the correct files to the Maxthon folders.
If you do try it, it would nice to get some feedback if it all went smoothly.
Link to VirusTotal Scan: https://www.virustotal.com/en/file/15807b67a026c22bb88e93ab15d052c4cdc4d2e172013d0ee653a9bba9da2fdd/analysis/1478411287/
Gets 2 fails from some random scanners... not sure why.
MX Flash Updater_0.65b.exe