Views : Make a block related to a page (with flag/addthis/privatemsg as fields in this block)
I found a way this week to get the good behavior.

i understood my mistake! My url was like that www.example.com/my-product/2 (made with pathauto)

When i selected content ID from URL my block was empty because he couldn't retrieve the good argument from the url (because my node id was in second position)
But when i go to www.example.com/node/2 it works fine

To resolve my problem i select raw value from URL  instead of content ID from URL (because with that option we can select which argument we want to retrieve --that was the second for me because of my custom url) 

In summary i follow this step :


Add contextual filter : content: nid
click on it, go to WHEN THE FILTER VALUE IS NOT AVAILABLE
Click on Provide default value
Select raw value from URL
Select the argument you want to retrieve from the url (path component)
I check Specify validation criteria
Validator : content
Filter value format : node id
Action to take if filter value does not validate : no result


It was a stupid mistake :) but i learn some stuff :)