Installation

Go to Mansur-Rig.com and create an account (if you haven't already).
Log in to your account.
You will be automatically given a free Mansur-Rig unlimited license.
Download the latest version of Mansur-Rig.
Extract the .zip library to your preferred location.
If you have another version already installed, preferably extract to the same location (version root folder should be placed in the same root folder of the previous version)
.../ANY_DIRECTORY
- .../ANY_DIRECTORY/mansurRig_1.0.1
- .../ANY_DIRECTORY/mansurRig_1.0.2
- .../ANY_DIRECTORY/mansurRig_1.0.3
Go into the main version directory
Drag and Drop the "mansurRig_DragAndDrop_install.mel" into any supported Maya version
Follow the prompt instructions
Restart Maya

Updates

Please make sure to update as appropriate. Version Updates Guide

Manual Installation

Download and extract Mansur-Rig as described above.
For the target Maya version, locate "Maya.env" file. For example (On Windows): "C:\Users\xxx\Documents\maya\2022\Maya.env"
Open the file for editting using any text editor software (e.g. Notepad)
Insert the following variable, changing the directory to your Mansur-Rig extracted version location: MAYA_MODULE_PATH = D:\mansurRig\mansurRig_1.3.6

Locate any installation directory of Mansur-Rig in your file system
Go into the main version (any version) directory
Drag and Drop the "mansurRig_DragAndDrop_UNINSTALL.mel" into any supported Maya version
Follow the prompt instructions
Restart Maya

As opposed to the Windows installer, the Linux version will install Mansur-Rig on the choosen maya version only.
The Linux installer is using the local Maya.env file to append the new envioronment variable instead of installing a system-wide persistant variable, as the installer can not assume system write permissions.
In case you want to install Mansur-Rig on multiple versions of Maya, please repeat the installation (drag-drop) on every required Maya version.