Plugin-container is used to load plugins separately so if a plugin crashes for any reason, Firefox won’t be affected by the crash and will stay responsive so here is the two procedures to disable the plugin-container.
Enter about:config in your address bar
Search for dom.ipc.plugins.enabled
Set their values to false
sometimes the above method doesn’t seem to work anymore with the newer versions of Firefox. so the first method did not work for you then follow the below 2nd method.
Right click on your computer icon on the desktop and click properties
Go to Advance system settings
Click the button called “Environment Variables”
Click the “New” button under User variables or System variables depending if you want the change to affect all the users on the system or just the one you are currently logged as
Set the variable name to MOZ_DISABLE_OOP_PLUGINS and its value to 1
Now simply restart Firefox and you will notice that the plugin-container.exe process will not be used any more.