Right click on the SC tray icon and select the item "Grab Windows Object or scrolling window" or hit default hotkey of Ctrl+Shift+PrtScr and then select the area to capture and follow instructions.
-mouser
The scrolling capture works but it is pretty complicated and not automated. In the Hypersnap program it is a simple Ctrl+Shift+S command with the cursor positioned in the window. It is limited to vertical scroll. If you want to terminate the capture, just use the Esc key.
-jojo99
Pros and cons.
From what I've read, if you want to do captures in browser, you're better off using a browser add-on (than any screen capture app), or, in FF at least, there's an inbuilt way of doing it (there is a thread here somewhere ... see
this dc post, and following posts).