iceweasel sometimes shows "untitled" when enter url

Hello,
In this week,after iceweasel is started,it shows "Looking up
www.google.com<http://www.xxx.com>"
in the status bar,but it doesn't connect to the home page,just shows
"(untitled)".It also happens when I open link in new tab or iceweasel failed
to refresh page to the new link I clicked in the current page.
This problem is very often.What may cause it?
Iceweasel version is 3.5.13 on Debian squeeze.