question: List the names of the browser that are compatible with both 'CACHEbox' and 'Fasterfox'.
#1 return browsers 
#2 return #1 that  are compatible with  'CACHEbox 
#3 return #1 that  are compatible with  'Fasterfox 
#4 return #1 in both #2 and #3 
#5 return the  names of #4