The word Tinderbox when referring to the application is, by common usage, often shortened to 'TB' in discussion in places like the user-to-user forum. This use of 'TB' is not an acronym. Rather, it is just a simple shorthand for those who find they need to type the word Tinderbox a lot!
It is also worth noting that the correct spelling of the application name is 'Tinderbox' and not 'TinderBox'. The latter is sometimes assumed from seeing the TB 'short' name.