NPGPX - the GPX plugin
NPGPX is a plugin that loads and displays GPX files directly in your browser window. It supports zooming and panning, as well as simple graphical settings. It should work with Mozilla and Mozilla-like browsers such as Firefox or Netscape.
GPX, or the GPS eXchange format, is an XML-based file format that is designed to store GPS data - waypoints, routes, and tracks. It is used by many GPS programs, for example Quantum GIS and GPSBabel. The specification of the GPX format, and other useful documentation, can be found here.
NPGPX is free software and is using the GNU General Public License. Basically this means that you are allowed to use, copy and redistribute NPGPX as much as you like. You are also allowed to modify it and redistribute the modified version, but only if you use the GNU General Public License for the modified version too.