Because Komodo is built on the Mozilla framework, it is necessary for us to include the Mozilla build that exactly matches the development version of Komodo. For that reason, even if you have Mozilla on your system, Komodo installs the Mozilla version that it requires.
Another sizable component of Komodo is language support. Komodo is so tightly integrated with Perl, Python, Ruby, PHP, etc. that it is necessary to include components of those languages, at specific version levels, for debugger and editor support.