Now, that is real coding !!!
In the beginning, It generated so many obstacles. First one was permissions: I use my laptop as second user so that I can stop spamming and unwanted installation by some websites without my permission. It was giving me "bad file number error" which I solved by running cmd prompt as administrator.
Second obstacle was to dive into massive code sea of Mozilla. It took me an hour to find the proper place for the code and to understand that code.
Logically I only need to find the Index of the current Tab. Then i need to insert a tab after that tab using tabContainer's insertBefore function. I thought these things would have worked. However, I red Aron's blog and came to know that I have to set the position variable to the currentTab+1.
This lab gave me a pretty good idea to work with real tree becasue I have only work with extensions. This will help me for my next project which is "Attachment Reminder."