Firefox Screenshots which lets you take, download and share screenshots in Firefox browser has recently got the ability to copy image to clipboard, now Mozilla has updated it to work in Private browsing mode.
Screenshots available in Nightly, works in Private browsing mode in Download-only mode, means, you can only download screenshots, but you can’t save and share screenshots.
Firefox Screenshots now works in Private browsing mode in Download-only mode
Another situation Screenshots automatically changes to Download-only mode is when you set Firefox to ‘never remember history’ state. You can do that by visiting Firefox Options > Privacy & Security, History> Never remember history.
Do note, Firefox Screenshots has this feature in Nightly, but not in Firefox 57. If you try to use Screenshots in Private Window in Firefox Quantum, the browser shows ‘Screenshots is disabled in private browsing mode’ message.
Bonus tip: If you use built-in Screenshot tool in Firefox often, click on three dots in URL bar to open Page Actions Menu, right click on ‘Take a Screenshot’ item and select ‘Add to Address bar’, or you can also use the option present in page context menu to open Screenshots.