+ Install 38 Alpha x86 from here https://portableapps.com/apps/internet/firefox_portable/test
+ open browser
+ set Options > General > When Firefox starts: Show my windows and tabs from last time
+ load at least one website
+ restart browser
Tabs from the previous session are appear as empty "New Tabs".
I first noticed this behaviour in 37 Nightly. However, this problem no longer exists in 37 Developer Edition. That makes me think the problem may be Electrolysis related...