The best way to disable the plugin check page is to update your plugins :) It leaves you vulnerable to various security threats when you don't update your plugins. Start with Java/flash/quicktime, etc.

If all plugins that are out of date are disabled it should not show that page

Firefox will still check for blocked and disabled plugins.
If you have any blocked plugins then try to remove them, so that Firefox doesn't find them.
You probably need to check the location in the pluginreg.dat file.

See "Manually uninstalling a plugin":

• https://support.mozilla.org/kb/Troubleshooting+plugins