[ubuntu] Thunderbird Updates

I am aware that Ubuntu runs a "custom" version of the Thunderbird (TB) email client (as it does for the Firefox browser).

My installed TB version is 38.6.0. The "mainstream" TB just released is 45.0. As updates are usually released to fix security related issues, is it safe for me to continue to use V.38.6.0?

I am assuming I could download TB V45.0 but am afraid I may break something as it is not the "custom" version for Ubuntu.

I ran software updater (14.04 LTS) and it reports this PCs software is up to date.

Comments, suggestions, guidance?