I've taken a look at Ezvid, which is a freebie that you can download. It's very similar to products such as BB Flashback (which is the tool that I use), except that it's entirely free. Ezvid is very advanced, and you can drop in your own images, music, rearrange sections of the video, choose parts of the screen to video, use a webcam and so on. It's not a browser based product, but to be honest, if you're after power and complexity, you're only going to get it with downloaded tools. This is certainly worth a look!