modular design: base plus browser, email etc

day by day the space and memory requirement is increasing exponentially. installing both browser and thunderbird is consuming a lot of space and ram. yes, i do use 80gb hdd.

is there any plan to seggregate base code and install browser, email client as plugins?

No. there are already a project that exist for this. use seamonkey instead. If you put Firefox and Thunderbird into one codebase, even using extension, their ability will be suppressed…