VLC is a free and open-source media player for Windows, Linux and Mac OS X. VLC includes a Web browser plug-in for Firefox, but it isn't installed by default. If you want to use the VLC media player plug-in to play videos embedded on Web pages in Firefox, you have to reinstall VLC with the Firefox plug-in. After it's reinstalled, you can modify the plug-ins and applications Firefox uses to handle media files on Web pages.
Download VLC's installer from VideoLAN.org.
Close Firefox by clicking the "Firefox" menu button at the upper left corner of the screen, and clicking "Exit."
Double-click the downloaded VLC .exe file, and follow the instructions on your screen until you reach the "Choose Components" screen. If you already have VLC installed, click "Yes" when you're asked to uninstall it first.
Click the check box to the left of "Mozilla Plugin" on the "Choose Components" screen of the installer.
Follow the instructions on your screen to finish installing VLC.
Click "Start," "All Programs," "Mozilla Firefox" and "Mozilla Firefox."
Click the "Firefox" menu button at the upper left corner of the Firefox window, and click "Options."
Click the "Applications" icon at the top of the Options window.
Click the "Action" menu to the right of each type of media file you want to play with the VLC plug-in in FIrefox, and click "Use VLC Multimedia Plug-in (in Firefox)" in the list of available actions.
Windows XP users may need to click the “File” menu to close Firefox and the “Tools” menu to open the Options window instead of clicking the “Firefox” menu button.