why don't you just use a "levels" adjustment layer ontop of the layer you need to select the brightest pixels from?
1. add levels adjustment layer ontop of the layer that you need to select the brightest pixels from
2. in the levels panel, pull the middle slider far to the right, but not all the way
3. pull the left slider just a bit to the left
now your image should be black, except for the bright pixels. You can tweak this to your needs by slightly moving those sliders again
4. merge the adjutsment layer with the layer below (your brightest pixel layer)
5. using the magic wand, select anywhere that is dark (black pixels)
6. invert your selection, and you now have the brightest pixles selected
I tried this on your "bubbles" image and it worked fine