hello, please go through the troubleshooting steps described at https://support.mozilla.org/en-US/kb/server-not-found-connection-problem#... (especially the part about dns prefetching & ipv6)

Be aware that you are using a Firefox beta release that may still have unresolved bugs.

Create a new profile as a test to check if your current profile is causing the problems.

See "Basic Troubleshooting: Make a new profile":

• https://support.mozilla.org/kb/Basic+Troubleshooting#w_8-make-a-new-profile

There may be extensions and plugins installed by default in a new profile, so check that in "Tools > Add-ons > Extensions & Plugins" in case there are still problems.

If the new profile works then you can transfer some files from the old profile to that new profile, but be careful not to copy corrupted files.

See:

• http://kb.mozillazine.org/Transferring_data_to_a_new_profile_-_Firefox

the problem still exist,thank you anyway

ok, then please also check that your firewall/security software isn't blocking or sandboxing firefox in any way. you might delete all rules for firefox and let the program detect it again.

Configure firewalls so that Firefox can access the Internet

another thing to try would be changing your system's dns-server to the one google is providing, for more information & instructions see: https://developers.google.com/speed/p.../using

ok thank you it looks like it was the DNS, thanks a lot