One night my firefox just started showing "Server not found" for all websites (i.e. "Firefox can't find the server at www.mozilla.com."). I noticed that it can find websites if make an entry in the /etc/hosts-file.
I have already started firefox in safe mode, the problem persisted.
I removed my ~/.mozilla folder entirely, didn't help either.
At this point I noticed that thunderbird was having the same problem and assumed it must be a shared library. I'm running gentoo linux, where the packages are distributes as source code, if available, so I started rebuilding each and every package on my system ("emerge -av --emptytree world"), still the same error.
I then tried installing the source-package of firefox (I was using the binary package "firefox-bin"), but that still didn't help.
Does anyone have an idea what I might do next?
EDIT (Thx, Gilles)
Installed Konqueror and verified that it doesn't have this issue (running fluxbox.)
I have manually set the proxy settings of firefox to "No Proxy", no change.
I have disabled ipv6 in
about:config, still the same.