Plugger is a plug-in for your Netscape/Mozilla on Linux that lets you run a variety of multimedia helpers as plug-ins for embedded content. Note that you can't just do this by setting up the helper apps directly. This is worth a look if only for their list of links to Linux multimedia players, including XAnim, which claims support for playing QuickTime and AVI files, among other things. I can't say I've had complete success with either, yet, but Netscape's plug-in recommender says "Plugger" for pretty much everything.