getting screenshots without using a plugin or website

First, open developer toolbar / inspector and type these commands into command line but make sure you're NOT in console. 

Browser toolbar commands start with a colon, and :screenshot is the one you want. 
:screenshot --fullpage
:screenshot --fullpage --clipboard
:screenshot --selector ".classname"

--selector will screenshot just one HTML element using the className CSS selector. 
You can also just include the screenshot button on the toolbar. 
Firefox does collect some data baout the screenshots.