Edit: Updated to TarxUI2. Download has been updated as well. See the last page for details.
1) Create a new profile. Go to settings, turn on GMCP.
2b) To install m-mf, pick your class, download the file, open your profile in Mudlet, click Package Manager, click Install, install the downloaded file. It'll run through, do its stuff. Once it says it's done and starts spamming, qq and close Mudlet. Reopen your profile. Run mminstall and follow the instructions.
4) At this point, I'd recommend quitting Mudlet. Open and login again, and everything should be working fine.