I never got any answer for this problem, but the problem is still here. It seems - to be confirmed - that if you have the option "customers have to be logged on to browse the shop" selected, going to maintenance will give an error message. With the new version of FF, the error is now :

Redirect Loop

Firefox has detected that the server is redirecting the request for this address in a way that will never complete.

The browser has stopped trying to retrieve the requested item. The site is redirecting the request in a way that will never complete.
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Anyone has seen such problem ? I use the latest ZC version...

sanji