|I think, if the RAM is wrong, the computer should not boot at all.|
If only facebook and nothing else ( other programs may crash, too. It should be only a matter of time. ) is crashing, this may mean that facebook is being allocated a memory space ( address area ) in the new RAM range and the new RAM stick is defective.
What I may suggest is, switch the old and new RAM stick positions and test your computer to see if other programs start to crash, too. Alternatively, you can make a bootable RAM test CD such as the one here and boot to it and test your RAM for quite a long time until you are sure about your RAM.