Proxy server check mark on always after restar of the computer

[styr]

Hi,
I have a problem and don't know where to go with.
I'm using Mozilla Firefox and I found out after each restart of my computer the proxy server for the LAN is check mark on in Local area Network in Internet explorer.(automatically switching on)
That unable me to connect to internet via Mozilla or Internet explorer.
Please advise me what to change since is very annoying.
Thanks
Adam