Everyone sems ot be having issues with this. In order to get your post id go to the posts or pages in the admin panel of your site (Mozilla and IE)and right click on the link and go down to properties, you should see the link https://homepage/wp-admin/post.php?post=10&action=edit
Your page ID is post=10.
In Chrome you hve to go down to “Inspect Elements” and find the a simlar link as the one above with the individual post number.
Not to sure about Macs so maybe someone else can it explain it.