Performance Alert - High Memory Usage

Hi,

 

I have been getting a Norton Performance Alert lately telling me that Mozilla Firefox is using high memory.  When I click on "Details and Settings", it tells me Firefox is using anywhere between 50-80 MB.  Mozilla says normal Firefox operation uses 120-150 MB?  Why is Norton alerting me to this when the memory usage seems low?  And why are these warnings all of a sudden popping up after using NIS and Firefox on this computer for years with no memory issues?

 

Thanks!