Hello,
Thank you very much 
I always keep the default settings in AVAST.
So I don’t understand.
I don’t understand why the speedtest on Firefox (I only use Firefox) is more better with KASPERSKY that is too heavy. As I already wrote, with KASPERSKY I had between 9 and 9.5 Mbps. With AVAST I have between 4.5 and 5.5 Mbps
And I have no problems with Youtube with KASPERSKY 
I tried to disable the web shield, it is a little better but it is still slow 
I disabled the script shield, the videos seems to buffer a little faster, but it is not as fast as with KASPERSKY 
So I don’t know what to do 
Thank you very much,