Taking a Screenshot; Windows > Start > search box > Snip. Select Snipping Tool. Use a compressed image type like PNG or JPG to save the screenshot. Save the picture(s) to your desktop. Press the Reply button. Then press the Add images; Browse button.

I'm seeing not much if I visit this link. Do you need to login to get that page with some data on it ?

Does this only happen in the Nightly build you use or also in the current Firefox release ?

Actually the URL I visited contained a parameter in the "&c=" query string but that page is no longer available. The webpage was longer than my screen (I had to scroll down to see the full webpage). So as I saw on https://screenshots.firefox.com/ Firefox can take a screenshot of a full page which includes the section that is visible on the screen and the invisible sections that are above and below the visible section. But the full page screenshot didn't work on the given URL for some reason.

I haven't tried this in the current Firefox release.

This issue is irrelevant by now.

This question thread can be closed now as the issue can't be reproduced.