I've just released Mastodon De-Mob, an anti-harassment tool that lets users to block everyone who favorited or boosted a toot calling for harassment. https://mastodon-de-mob.codesections.com/
Please feel free to test it out with the example URL I provided; that will only block a test account I set up for this purpose. Hopefully, you won't ever need it for real.
It also reports the harassing toot, which I hope will prevent the tool's abuse for non-harassing toots.