Files with the .m2s extension belong the web-browser 'Maxthon', a full-featured web-browser for the Windows operating system.

These .m2s files are used to change the default visual theme of 'Maxthon' and usually contain a collection of images and a settings file.

These files are archived in the standard zip format so can be extracted using an archiving program such as WinRAR, however they should primarily be opened by Maxthon by either double clicking the .m2s file or locating the file within your Maxthon browser by selecting view > skins > manage skins.