[gentoo-user] Blocking certain sites the easy way ?

Hi,

With wireshark I found, that firefox accesses sites on startup, from
which I dont know, for what reason this access is needed or whether
the NSA, CIA, FBI, BDN, MOSSAD (fill in what organisation you ever
suspect to do such things) has invaded my PC.

I want to block such accesses for two reasons: First is ...hmmm...
to block that accesses...second is to find out what will not work
than.

I dont want to install and configure a complete full blown firewalled
SEL-Linux thingy here and I dont want to reboot my Linux box for every
new site I added. I am looking for a simple solution, which I can use
without studying the history of TCP/IP and others... ;)))

What can I use for this purpose?

Thank you very much in advance for any help!
Best regards,
Meino