Mozilla in their infinite wisdom have decided to unilaterally switch on "Clear history when Firefox closes" for Cache, Site Preferences and Offline Web Site Data as shown here.
![Clear_History.png](https://preview.ibb.co/gaQsBG/Clear_History.png)
If you want FSH to remember certain preferences and logs then you will have to turn this back off again. You can find it in Options -> Privacy & Security.
Luckily this only effects the parts of FSH that have been migrated to the newer storage model. Things like the new guild log, monster log, combat log, buff log, fsbox log, your preferences for guild, individual, composed potion inventories and the arena.
I suspect that the reason they have done this is because they are working on a new storage API which will allow websites to ask for permission to permanently store data. This is a 'Good ThingĀ®'. One day in the future FSH will be able to explicitly ask for your permission to store data.
However, the new storage API isn't ready yet. Even if it was, web site developers would need time to re-engineer their code.