Grossu, you may be having a problem with your internet connection. In my experience, this happens when the bandwidth is ''chocked'', which often occurs when you are using download accelerators, download managers or other software that ''steals'' all the bandwidth for itself. You may also be having a problem with some extension or plugin that is hindering your Firefox's normal behavior. Have you tried disabling all add-ons (just to check), to see if Firefox goes back to normal?