Made an account just so I could rate this.

The delay page really is the killer feature for me. I can set the timer to just long enough so that I stop the impulsion, but just short enough so that if I really need to access something during the block period I can, if I feel like waiting (which I usually don't). Alt-tabbing also cancels the countdown by default. The statistics breakdown for each blocking group is also brilliant.

There's a lot more features to this extension I haven't tried, but for now the way I have it set up works really well.

All of this under a copyleft license means a big thumbs up from me. I can't give enough praise!