I observed something similar several years ago: http://www.overclockers.com/forums/showthread.php/697061-Whe...

I still think the worry about it wearing out an SSD is overblown. The 20GB per day of writes is extremely conservative and mostly there to avoid more pathological use cases. Like taking a consumer SSD and using it as the drive for some write heavy database load with 10x+ write amplification and when you wear it out demand a new one on warranty.

Backing up the session is still sequential writes so write amplification is minimal. After discovering the issue I did nothing and just left Firefox there wearing on my SSD. I'll still die of old age before Firefox can wear it out.