Well I never asked for it and I never got it, until I actually physically downloaded it for testing and uninstalled it after testing. I have Firefox as my default browser and even when Avast Secure Browser (ASB) it never impacted on my Firefox installation.
The Avast Secure Browser is a stand alone product and you would have had to downloaded or accepted (in some way) it as a trial for it to have been installed.
That aside, ASB can be removed in the same way as other programs from the windows control panel add remove programs.