A quick history of web browsers:
In the early 90's there was a browser called NCSA Mosaic which is very basic by todays standards but was the first fully functional graphical web browser. It was very popular until a company called Netscape came along and created the Netscape browser which, by version 2.0, had taken nearly all the marketshare. Around the mid 90's a company called Microsoft decided it wanted to get into the browser industry as well and introduced Internet Explorer, which was nothing more than a hack job on Mosaic (and is to this day). By the late 90's MS decided it didn't have enough of the market share and "innovated" by integrating IE into the Windows interface and that quickly caused Netscape to loose all it's market share to MS. Netscape decided to start an open-source project, named Mozilla (after their mascot), to improve the Netscape engine. Right before the release of Netscape 5.0, the Mozilla project decided the original Netscape engine was at it's limits and couldn't be improved upon any further and scrapped the whole thing (and Netscape 5) and wrote a completely new engine called Gecko which would power the open source browser Mozilla and the proprietary browser Netscape. The Mozilla project eventually got to version 0.9 of the Mozilla and Netscape 6 was released and then it hit 1.0 and Netscape 7 was released. Around Mozilla 1.2 people started becoming concerned about the bloat of Mozilla and started a new project, Firefox to write a lighter, faster web browser based on Gecko.