firefox high cpu and memory - unsolved

I don't find the reason why Firefox asks so much CPU when starting and why it asks so much memory. Memory consuption only increases, and with 4 different tabs with a flash game it was asking 500-600 MBs of memory...

Whe used to love Firefox, and we still do. At least for me, it gonna be hard to not use Firefox browser... but memory consumption is really low with Internet Explorer, Chrome or GreenBrowser. I don't understand how Firefox can ask so much memory...

I don't have any virus acording to Malwarebytes or Microsoft Security Essentials...

And not even strange add-ons installed...

Only with flash games on 4 browsers:

Firefox not only needs 300k memory but also the flashplayerplugin is asking 290k of memory...