When I am eating at a table that has crumbs from mezonot and I am eating a salad, can I bless mezonot as well, in case mezonot could have dropped in?

One should only make a Mezonot Bracha if the Mezonot part of the food is an important part of the food even if it is not the majority of the food. Crumbs are meaningless. There for you should make only an Adama Bracha on the salad. Rabbi Yitzchak Grinblat.