Sorry about HB not working after the update. Likely, you are going from 1.x to 2.0.0, right? The way that addons store data has changed significantly since the legacy version, and as such upgrading does cause the blacklist to get forgotten. It CAN be recovered if you follow the instructions from https://github.com/kainsavage/HistoryBlock/tree/v2.1.0#migrating-legacy-blacklist
Please let me know if I am misunderstanding and file a bug report with as much detail as possible on Github.
Excellent add-on, but really need to turn off or drop the "block this" button... I mean, I close the tab, someone comes in, we start using the computer and he/she sees the block this button and ask what is it... kinda "raises some flags" I think.