If you use firefox,

https://addons.mozilla.org/en-US/firefox/addon/leechblock/

https://addons.mozilla.org/en-US/firefox/addon/blocksite/



If you want facebook widgets blocked on other pages, use the adblock or adblock plus extension with chrome or firefox and add these custom rules:

||facebook.com^$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
||facebook.net^$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
||fbcdn.com^$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net
||fbcdn.net^$domain=~facebook.com|~facebook.net|~fbcdn.com|~fbcdn.net

Those should block all facebook stuff on non-facebook sites.  Except on sites you've whitelisted in adblock.