Well, I just went to my Firefox's local user profile, found extensions directory and VM's plugin.
C:\Documents and Settings\kamil\Dane aplikacji\Mozilla\Firefox\Profiles\2qr71loy.default\extensions\VMwareVMRC@vmware.com)
Edited 'install.rdf' file. Found a section:
<Description>
<em:id>{ec8030f7-c20a-464f-9b0e-13a3a9e97384}</em:id>
<em:minVersion>1.0</em:minVersion>
<em:maxVersion>3.0.0.*</em:maxVersion>
</Description>
</em:targetApplication>
And just changed 3.0.0 to 3.0.1
And Voila, restart firefox and got VM plugin working again