I'm now online in Linux using Mozilla :D
 

I found some similar pages as well... the problem is definitely D-Link DSL-504T ADSL Router that I use and ...

1- I set the DNS server in the router manually but it didn't solve the problem.

2- tried to update the firmware on my router but it failed (several times) and after that I lost my connection in XP as well! restored to factory defaults and could connect through XP again.

3- found the thread 525728 in this forum and disabled IPv6 in Mozilla as it says ... Result: PROBLEM HAS BEEN SOLVED :)

Thanks everybody!

that's really weird, think i've seen the same thing before on here and been unable to help. seems worth remembering...

I know I'm jumping in late, but let me chime in anyway. I had the same problem on my T41 laptop running FC6. Websites were mostly inaccessible via name, while access via IP numbers always worked. I found that the best time to attempt connecting to a site is just after boot and connecting to the network; after maybe 10 minutes nothing was accessible anymore. Turning off IPv6 helped just a little bit - a few more sites were accessible, and for a bit longer. Sometimes a site would load after a few presses of the "try again" button in Firefox. I should say that ssh suffered from the same problem (could not reach remote hosts by name, while IP numbers worked very well). It felt a bit like the DNS server was, most of the time, taking too long to respond.

I tried booting the ubuntu live CDs 6.06 and 6.10 - in both cases internet access worked flawlessly, so at least in my case it's not a Windows vs. Linux vs. router issue.

What solved the problem completely and instantly was to turn off NetworkManager (System->Services->NetworkManager off)(in addition to keeping IPv6 off). In Services->Network I simply configure my preferred access point.. and voila, all sites load instantly in firefox. No more automatic switching, but heck, I can live with that :)

Hope that helps.