Mozilla sees no future for Thunderbird and has thus decided to cut off the ties with this stand-alone email client. Mozilla however stop active development of in 2012 and now the company wants to split off completely. 
In a long post to Google Groups, Mozilla Foundation executive chairwoman Mitchell Baker said,
I believe Thunderbird would thrive best by separating itself from reliance on Mozilla development systems and in some cases. The current setting isn’t stable, and we should start actively looking into how we can transition in an orderly way to a future where Thunderbird and Firefox are un-coupled.
Giving the reasons of this spit off, Baker said that they want to remove Thunderbird for good. He further added that the competing demands are not good for either project. She writes, “Neither project can focus wholeheartedly on what is best for it.” Mozilla basically wants their engineers to focus on Firefox and its web driven changes.
Thunderbird released as an open source email client in 2003 was initially very popular among the internet lovers but soon the users started using the web platforms for their email needs. However, Thunderbird still has a huge fan following and Mitchell Baker believes that it will thrive best if separated.
There is no official word from Mozilla if the company will make it a distinct open-source project or will outsource it to some other software community.
