Yesterday while I closed Firefox (latest 10.1), I noticed Firefox window left behind, which was just some popup browser window from Google when I tested a page design (how would it look on a mobile phone). So I closed that window afterwards also.
Today I open Firefox and instead expected leftover tabs, I see only this tiny Firefox window (from phone design test), without tabs. Even more importantly I had tab groups which also disappeared, just because I forgot that browser popup window was left behind before closing Firefox.
Can I restore group tabs?