Before you go too far down the road you're on, consider researching the Graph API a bit to see if it can do what you want. If it can, it will be much easier and more accurate. I think. Here is a starting point: Search messages FQL on SO (FQL is deprecated but will apparently still work as of now) and Facebook+Graph on metacpan. This is interesting to me so I might play with the problem but I'm also pretty booked up so if I don't come back with some snippets tonight, :P

Update: this path is probably not any easier since it looks like you have to wrap anything you want to do in "an app." Not impossible or super hard but a pain if you already have the HTML.