Though Eclipse is primarily known as a Java IDE, its openness and extensiblity make it effective for writing code in other languages as well (assuming an appropriate plugin exists). If nothing else, Eclipse's GUI provides an interface to CVS and Ant that is easier to use than their command-line counterparts.
Although creating a Mozilla/Firefox extension has nothing to do with Java (though it does require building a jar file), Ant is an appropriate build tool to use because of its cross-platform support.
CVS seems to work well enough, so there has been no motivation to replace it with Subversion or RCS yet. Further, Eclipse's built-in support for CVS increases the attraction in using it over other version control systems.
Maven generated the HTML for this web site from a collection of XML files. From its web site, Maven appears to be useful for automating other tasks as well; however, its primary role in the Google Dominoes project is to generate pretty HTML pages.