Hi solarblue,
what exactly is the problem? Could you please provide more details? For example, how do you run through the advanced configuration options of the router?

Two things happen. When you try to configure the router you receive micro http errors. If you hit the refresh several times the screen eventually comes up. I can provide a screen shot if you would like.

The second and more important issue is when I follow the instructions at http://qwest.centurylink.com/internethelp/modem-q1000-adv-dmz.html and press the apply button, the DMZ will not activate. It consistently goes back to the same configuration page but will not save changes in the modem.

Your connection is via wireless or via ethernet?

I am not sure! Maybe you could try to upgrade your firware upgrade firmware in case you have not done so already. Another action I would take is to check if any application/firewall prevents firefox from correctly communicating to the specified address.
Maybe someone else could help further!

I connect via ethernet cable directly into the modem. There is no firewall blocking or port issues as the config works perfectly if I use IE.

I validated that I have the latest version of the Actiontec firmware on the modem.

I'm on the latest firmware updates. This seems to have been happening since firefox 15 or so I'm not exactly sure. It might be how firefox handles responses to forms? Firefox use to work with these but it hasn't for a while now. I work with a lot of routers I think this also has a problem with some linksys routers as well. I am willing to send any information you can use to help fix this problem. Since I work with Centurylink a lot and firefox is my choice browser I want this fixed.

Details of problem: When I make changes on the selection page and submit it. Some of the changes are ignored by the router.

Example: When I go to edit the redirected ports. It ignores my changes unless I submit the page and resubmit the page right after it sometimes gets it to it. weird behavior.