There are times when you may want to find out since when you are a facebook friend with some one on facebook, together tagged photos in which you both appear or all those conversation on facebook both of you commented. This feature of facebook is called the common interest feature which lets you find all those things like mutual friends, common pictures and common facebook both the facebook users like.
Please note that in order to find common interest in between two facebook users they are not required to be friends with each other but they can be friends with each other on facebook. Follow the procedure below to know how to use this feature.
1. Login to facebook.com
2. Go the specific person facebook profile with which you want to find out similarities.
3. Copy the profile id or facebook user name from the profile URL as shown in the image below.
Note: If the facebook user has not already created the vanity url for his/her facebook url you will see the facebook profile id, In such case copy the profile id as shown in the image below.
4. Now put the facebook profile id or the user name for both the people on among which you would like to find similarities in the format URL below.
http://www.facebook.com/<facebook user id 1>?and=<facebook user id 2>
The URL above will show the similarities among me and my friend sumit, as you can see in the image below.