A webm file can be operated with Firefox, Google, Chrome, Opera etc. This can also be operated in the Safari Web Browser on a Mac. The same can be achieved in multiple ways. First of all, one has to go through VLC. Then from VLC rout, one has to search the VLC for Mac OS X and then one needs go for the plug in operation.
If one is on Mac, one can use most of the programmes supported by Windows to play the Webm file apart from free EI media player.
If one is interested to open Webm files on one's iOS device, this can be done through player Xtreme Media Player or through the VLC apparatus.
In order to use Webm file with a particular programme or device not supporting the format, one can convert the video to a file format supported by a free video file converter programme.