Firefox freezes when using special ports (which are inaccessible by the current network)

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What steps will reproduce the problem?
1. configure opsview on a special port (e.g. 3000)
2. configure nagioschecker to that
3. configure your router/network blocking that port (out)

What is the expected output?
After a timeout maybe a little error sign aside the nagioschecker bar.

What do you see instead?
Firefox freezes from start on. You can scroll up and down (for the default 
homepage), but you're unable to open or close a tab, click on a link or click 
on any menu buttons. It just happens nothing - like completely frozen.

What version of the product are you using (Nagios Checker and Nagios)? On what 
operating system?
Nagios Checker 0.16 for opsview 20120424 with Firefox 12.0 on Linux Mint 12 (~ 
Ubuntu Oneiric)

Please provide any additional information below.
I think it just doesn't detect, that the webinterface is not accessible while 
the rest (http, https) works just fine. This happens everytime in the study 
network, so I think its because of the port (which is blocked).
Workaround to get firefox working for the moment by disabling nagios checker: 
Disconnect your notebook/computer from the network, then (re)start firefox. 
Because now nothing hangs, you can disable nagios checker in addons.

Original issue reported on code.google.com by dragon.d...@gmail.com on 14 May 2012 at 2:37