I think that sentence should say "[...] by making small changes in Mozilla Firefox".
Rationale: Only three things have ever formally used the term "Mozilla" alone: 1. the codename for the Netscape Navigator software project 2. the official, public, original name of the Mozilla Application Suite<http://en.wikipedia.org/wiki/Mozilla_Application_Suite>, currently known as SeaMonkey <http://en.wikipedia.org/wiki/SeaMonkey> 3. the Mascot of Netscape. Source: http://en.wikipedia.org/wiki/Mozilla and what people have said throughout the years. Saying "by making small changes in Mozilla" basically means "changes in Mozilla as in Mozilla Application Suite" (other two, or Mozilla Foundation/Mozilla Corporation make no sense here).
-- http://gnuzilla.gnu.org
