Hi Username, just a quick feedback:
1. I have to use the "gksudo" command in order to get proper privileges
2. even with the proper privileges the "nano/etc/host" command doesn't allow me to save changes
3. the "gedit/etc/host" command works and I can save changes , BUT

4. it doesn't block Facebook. Same problem as on Windows. You can't block https websites (I guess that's the problem). One would need a little program like "K9" which does the job perfectly on windows. Sadly it's not available for Ubuntu. Are there any other ways ?????

There is an add-on for firefox available called "Block-Site". Is that working for https sites ? Is it working for the guest account ?

Thanx. It's very difficult if not impossible to change the settings on the Ubuntu guest account. An add-on called Block-Site 1.1 works perfectly for the administrative account but not for the guest account. I'l do it the easy way now and will delete the original Ubuntu guest account and open a customized guest account even though I'm going to lose all the advantages of the original Ubuntu guest account. Thanx for your help anyway.

AHHHHHHHHHHHHHH, I made it. And NOW: