Capture Web Page Region - lets you choose whatever size region that will be saved as a screenshot. Capture Whole Web Page - does what it says, takes a screenshot of the entire web page/tab that you're on. Capture Visible Web Content - does above, with exceptions, I'm not too sure. I'm assuming security exceptions.

There are some similarly named extensions. Perhaps you meant to get this one: Web Clipper: Easy Screenshot?

You also could try out the built-in Firefox Screenshots tool. This is only enabled on a subset of Firefox 54 users because it's still in beta testing. More info on the features: https://screenshots.firefox.com/

Here's how you can turn it on:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste shot and pause while the list is filtered

(3) Double-click the extensions.screenshots.system-disabled preference to switch the value from true to false (disabled => false = enabled => true)

A new scissors icon should appear on the main toolbar. Screenshots are (according to the site) saved online for two weeks. While I think the addresses would be hard to guess, I wouldn't use this for any pages with highly sensitive information, just in case.

Also, users have observed that very long pages are not captured completely in this release. You still need an extension for those until the updated version gets shipped (maybe in Firefox 55?).

Thanks for this info!