Hi Leo2, thanks for the feedback.
The v2 version is a complete rewrite of the v1 version to stay compatible with Firefox 57. Given that I'd never used the closed tabs list, I seem to have forgotten some things. Will fix them soon.

Regarding the max # of closed tabs setting: Did you actually use this? I assumed that most people would either want all their closed tabs to be saved or none. Currently, Dustman simply saves the last 100 tabs, and forgets the others if the appropriate setting is checked. Would you rather set a bigger (reasonable) limit, say 1000?

Answer to update (wow, the comment system is inconvenient here!): Sure, I will take care of it in the next few days.

Update 2: I think both issues should be fixed now.