Memory occupancy rise persistently In Dojo 1.0.2

Hello:

I am using dojo 1.0.2 in my web site,

and the memory occupancy rise persistently,

but the status of the FF progress is still sleeping, the percentage of cpu occupancy is still zero.

I don't know why does the memory occupancy rise while FF progress is sleeping.

it is so strange to me and can not understand.