Yes , i did this things, i have my pc with the proxy configured that have the port 8080(set it in zentyal) and with this i have internet(the proxy is working) if i put in http proxy general to always deny i dont have internet (it works) but if i want to restrict only some sites it doesnt works. i Readed this docs.
I dont want to use the groups because a lot of employees dont use their credentials to log on(use ubuntu) so i think that it wouldnt work, i only want to that all the machines that are conected to the proxy(manually configured) cant enter to facebook, hotmail ,and some other pages. The others machines will conect without the proxy and have to access the internet without restriction.
Thanks