Do fórum de ajuda do Mozilla :
Firefox 3.6+ versions do prevent plugins from being installed to the \Program Files\Firefox\plugins folder to keep plugins out of Firefox, but that isn't how most plugins get "into Firefox". Firefox scans the Windows Registry for plugins that have the correct Registry key for Firefox, and uses those plugins from wherever thay are located on your hard drive. Once the program using that plugin is installed, and the Registry Key is set, all you can do is physically remove the plugin files or turn off the plugin in Tools > Addons > Plugins Sorry, I don't know how plugins are handled in Linux OS's. Impossible to prevent the programs you are installing from installing their plugins for Firefox. Once you give a program permission to install on your PC, it can do anything it wants with Firefox or any other program.