Step 1: use Firefox, and add the "Pixlr Grabber" plugin.
Step 2: Pixlr Grabber lets you take a snapshot of any portion of a web page - even stuff below the bottom of the screen.
Step 3: Take your screenshot, and select "Copy to clipboard"
Step 4: Waltz over to Confluence, and simply PASTE that screenshot into your wiki page. Resize as necessary.