As it is now the header gets placed in the middle of your shot if you try to take a full page shot
I have this issue too.
I use this tool to capture the full page of firefox as an image, but now days lots of pages use the sticky menu and it follows you while you scroll down ending somewhere in the middle of the last screenshot part.
One way to solve this could be to make the screenshot buttons sticky too so when you rescroll to the top of the page the menu is back in place and you still have access to the buttons so you can save your screenshot.
Edit: I have to change my entire post because I didn’t see that my workaround doesn’t work.
Yes, when selecting an entire page (no matter how it’s accomplished), we have to scroll all the way down in order to click Download or Save. That’s not good.
ScreenGrab still seems to be far better.