Follow-up Rated 5 out of 5 stars
I found that TableTools2 suddenly had disappeared.
Turns out that in "synchronizing extensions" between two machines, I had Book Text Mark" extension enabled.
Apparently there is an incompaibility with TT2 not showing up in the context menu any more.
Since I don't need to bookmark "a text within a long page" too often,I disabled BTM and ... TT2 is back.
Hmm, I tried installing BTM and it seemed fine. TT2 still showed up in context menu. I wonder if some other addon's actually causing BTM disabling TT2 in context menu?