Absterge works such that a user logs in to the Facebook Timeline, and navigates to the 'Activity Log' section. The removal process automatically unrolls all user's activity (by triggering click to "More Activity" link), and then removes every activity that can be removed from the logs. The only required user's activity so far is to expand the year where the logs are chronologically classified. The script deletes everything.
The script is in the initial version, therefore I demand your patience. Note that, once you open the 'Activity Log', the script will delete every Facebook activity visible in the expanded chronological year. How to use it:
1. Install Firefox (any OS on any architecture)
2. Install Greasemonkey
3. Download and install the Absterge script available above.
4. Log in to Facebook and make sure that Facebook Timeline is available.
5. Navigate to the 'Activity Log'.
6. The script will start unrolling the current expanded year triggering the 'More Activity' click event.
7. As soon as the script finds posts / comments / status updates, those will be automatically removed, without warnings.
8. In order to remove the activity of another year, just expand the year tab. The script will take care of the rest.
The current implementation is quite sloppy. It would be great if someone is in the mood to adapt the script, so it can have a nice GUI to integrate in the Activity Log of Facebook, as well as to provide feedback of the posts being removed.