I am sorry for the confusion. I am translating from the french edition of the software. I tried both these options with the same result:

1- Last item (under the about Avast) in the right-click icon menu that can be translate I guess by “Stop the permanent protection”. A red circle appears on the icon.
2- First item in the icon right-click menu that can be translate by “Management of the permanent protection”. Then I paused and/or terminated every services.

Both time, I was left without protection, still with some processing by ashServ.exe and, most importantly, still with my really choppy browsing.

I tried your suggestion (stopping the services from the Administrative Tools). It did indeed killed all sign of processing by Avast, but the problem remained entirely.

Once again, I then unsinstalled Avast from the computer and the problem was solved.

By Eddy’s words: Very strange.

Thanks anyway vlk for your precious time.
Symont