I disagree. An immediate action is essentially an interrupt. It happens immediately.
So as you see that death ray coming your way, you can pop the emergency force sphere. Same as if you were falling off a cliff, you can pop feather fall before you hit the ground.
Immediate Actions =/= Attacks of Opportunity
An attack of opportunity "interrupts" the normal flow of actions in the round. If an attack of opportunity is provoked, immediately resolve the attack of opportunity, then continue with the next character's turn (or complete the current turn, if the attack of opportunity was provoked in the midst of a character's turn).
So, the death ray/fire ball/disintegrate/blade barrier/whatever would hit you. THEN you could use your immediate action to cast EFS.