- Firefox: Type about:plugins in the Location Bar (address bar) and press the Enter key.
- Mozila Suite / SeaMonkey: Open the Help menu and choose "About Plug-ins".
Note: Starting in Firefox 3 and SeaMonkey 2, disabling a plugin via "Tools -> Add-ons (or Add-on Manager) -> Plugins" will remove it from the about:plugins list; re-enabling a disabled plugin will add it back to the list.
To show the full path to the plugin instead of just the file name, type about:config in the address bar and press the Enter key. Find the preference plugin.expose_full_path and change the value to true (double-clicking the preference name will toggle the setting). Caution: Exposing the full plugin path can have security implications on some systems.  It's best to reset the preference to the default "false" value when you are done.
- This screenshot shows the beginning portion of an about:plugins list in Firefox 4, on Windows 7.
In some cases, about:plugins may display outdated information, even after a restart. To refresh the list, close your Mozilla application and delete (or rename) the file "pluginreg.dat" (see the profile folder article for the location). The file will be generated.  
Related bug reports
- Bug 236201 - about:plugins lies to user about available plugins
- Bug 313700 - Stale information in about:plugins (pluginreg.dat) after a plugin update
- Bug 488181 - simplify code for exposing plugin paths/names
- Bug 548481 - about:plugins page title should be "Enabled Plugins", not "Installed Plugins" (Fixed in Firefox 3.7a3pre and above)