I do not see Calendar tab in Thunderbird at all. I tried v8 and v10 beta but same issue. Please help resolve.
I have installed all addons as well, it was working for me when I was using TB 5.
Well found the problem or atleast it is fixed now, installed xul-ext-lightning package and now things are working fine.
You do have the correct Lightning Add on installed? For Thunderbird 8 this would be 1.0 which would not work in 10beta I believe.