Adblock Plus has an option called "Show tabs on Flash and Java". When activated (the default) it will display a button saying "Block" at the upper right (lower right if there isn't enough space) corner of every object. Clicking this button will block the object.
Alternatively you can open the list of blockable items (press Ctrl+Shift+V or click the dropdown arrow next to the ABP toolbar icon and choose Open blockable items) and look for an object there.
You can click the Type column header — this will sort the list by type and make finding objects easier.