I don't know how many times I've had to paste together five screen captures to make a single image of a web page. For some reason, I never really went out looking for a solution. So, yesterday I had to do a bunch of these and finally decided that /someone/ must have come up with a good solution for this.
Yes they did.
This add-on is quite simple. You can either save a screen capture as a file or copy it to the clipboard. You also have the option of capturing a complete page, the visible section, a selection or the current window.