Since the plugin is a .xpi it requires XUL which MicroB doesn't use. There are some browsers available (based on Firefox) which do support XUL but this has a performance impact. To restate: MicroB != Firefox so MicroB isn't officially supported by this plugin. I read something about this plugin not working in older Firefox versions (3.0.x); MicroB is based upon on older Firefox version. The plugin will probably have to be ported in order to get it working. If you are a paying customer you're better off contacting VMware. What did they say?