Comment 5 for bug 197786

P.S. for any frustrated users finding this via a web search to completely disable the network manager check (a definite upgrade) then do the following. First make sure that there are no prism windows open.Then edit a file in your home directory called prefs.js located here .prism/<string-of-chars>.default/prefs.js Note that <string-of-chars> will be a random string of characters different to each person.

At the bottom of this file add the following line:

user_pref("toolkit.networkmanager.disable", true);

save the file and then try it out. The only possible downside is that you will get an error if not actually connected. IMO this is preferable to getting one no matter what.