Because of certain browsers incompatibility with the new technologies, certain commands are unavailable.
At a first look we thing that the commands are disabled but is not like that.
Below are two screenshots of the same page, but from different browsers: Mozilla Firefox (final version) and Internet Explorer 8.
In those images we see that we cannot access this documents library using Windows Explorer, because the Open with Explorer command is not active (first image – Mozilla).
Things changes when using Internet Explorer: the command is active (second image – IE8).
Below is a list with system requirements: operating system – browser.