This will depend on the browser you're using, & having flash installed on your android. For example, in Opera if I see a picture in forums that needs me to scroll to see all of it, then the thing to press is the arrow on the end of the scroll bar, not the scroll bar itself. It will then scroll over.
Mobile browsers won't have the same functionality as desktop computing, because they're meant to only offer the fundamental basics without bloating the system. In most phone browsers to save something you need to press & hold it for the prompt to appear; to play content you might need to press it twice (to activate the flash plugin, see above), or to scroll use the arrows (again, see above).
Bear in mind that mobile phone browsers are playing catch up to computers & only recently got it together with flash content, youtube intergration, etc etc, so are still a work in progress. For the most part, press & hold on an item would bring up a menu.
