i just got some ram for my new lifebook t902
you need to go to the spd tab on cpuz and see what memory dimms you have in there. there will be slot listings and a part#. ignore the jdec spec tables and look up the part#.
your upgrade options will depend on what configuration is in there. the default specs say 6gb, so if that is 4gb+2gb your option is to get another 4gb for 4+4(8total), or get 2x8gb for 16gb total and sell the old 4+2. if it is 3x2gb, you will have to source a triple channel set.
ddr3 1333 is the bottom speed now, you should have no problems finding it. the crucial config/tester is ok but obviously they only point you to their stuff. it didnt work for me because they dont have my model of lap(too new), they dont have any 1x4gb ddr3 1600 modules, they didnt have any 2x8gb ddr1333 either. they are cheaper though.
i found a exact match to the part# for mine on ebay. i went with this because i didnt want to be running back and forth from frys trying to see which 4gb sodimm would work with the one that came from the factory.