you are asking an awful lot of questoin with no sign of you having tried anything for each issue prior to asking... you should provide more information.. what have you already tried, what errors are you having etc... in this case, there are a myriad of extensions for firefox
https://addons.mozilla.org/en-US/firefox/ which you could use. blocking access on the client itself is a pretty poor idea though... you would just be able to uninstall the software to get access back or use a different browser. you might prefer somethign like dansguradian to control further down the line ...
