I'm on Ubuntu 14.04 LTS (workstation), and it's like Firefox is very slow (compared to the same on an old windows machine... sorry again for the reference, but I thought it would be as fast or faster than on windows). I haven't installed any add-ons or try to tune up by myself by the time.
Firefox is the 35.0.1 and thought it was slow on a Ubuntu 14.04 Server too. Is it something normal on Ubuntu?
Do I have to modify some settings on Firefox or Ubuntu to tune up this?
What is slow? Switching between tabs, opening a site, scrolling the window...? It might be your graphic drivers. If you have an nVidia card try installing the non-free nVidia drivers rather than the stock ones that come with Ubuntu.
UPDATE:
Okay, if it's the network access that is slow my guess would be that you have IPv6 enabled. Try running sudo apt-get update from a terminal window, and if you get the same 5-10 second pause then try disabling IPv6. The "quick" way to do that (just for testing) would be to edit /etc/gai.conf and add the following line to it:
precedence ::ffff:0:0/96 100
Restart firefox and see if that speeds things up. If it does, a better way to disable IPv6 is described in this answer to the question How to disable IPv6 in Ubuntu 14.04?
