OS : Linux 3.11.10-301.fc20.x86_64 [1] It is installed by Fedora-Live-Desktop-x86_64-20-1.iso [2] enviroment : gnome both the [1] ( fedoraDesktop I am using) and the [2] (Fedora-Live-Desktop CD system) have the same problem: when firefox loading a page can't be found or blocked , it will take a few seconds trying to open the page , during this time ,Fedora system become very slow, keybord response slow, mouse click response very very slow . some websites using web pages can't be found or blocked, loading these resources one by one will take a lot of time ,and the system will keep in a very slow status long time. when I were using windows xp/7 system , there isn't that problem ：open a page can't be found or blocked will take a while ,but the system won't slow down ,keybord and mouse action will be responsed very fast. last year when I were using Fedora 17(KDE) and 18(KDE), there isn't that problem I have tried to fix the problem , but can't solve it by following methods : 1.updated firefox to the latest version. 2. clean cache and history 3. disable IP v6 in network configure and about:config disable IP v6 4. disable smooth scorlling and hardware accerleration 5. disable some plugin and plugon 6. stop and remove firewall and restart system 7. Using live CD directly (Fedora-Live-Desktop-x86_64-20-1.iso) , do not install anything(software, plugin, etc) , do not update any thing ,use firefox directly , it's still have that problem ! I also tried another brower google-chrome ,It is also have the same problem ! I feel comfussed , I don't know it is a problem of firefox ?? or gnome ?? or fedora system ??