OK looking at the files detected, the important on is the rootkit agent one as if avast doesn't find the rootkit it hides other malware.
If avast doesn't find the files then it is also not going to detect any associated registry entries, so things sort of snowball. The problem is exacerbated when the system is already infected before avast gets installed.
If you had first posted the full log I would have suggested sending samples of the sfx.sys and sfx.dll to avast to help improve detections. Whilst it would be possible to restore them from the MBAM Quarantine, add it to the chest and send to Alwil (see below).
However, MBAM would restore it to the original location and as such there would be a limited risk since it is in that location. Since the associated registry entries to run these are still in quarantine the risk is low and once added to the chest you could run MBAM again to get it back in quarantine. If you aren't comfortable with that then forget it, but it is something to think of in the future, try to obtain samples to improve avast detection.
Add the file to the User Files (File, Add) section of the avast chest (if it isn't already there) where it can do no harm and send it from there. A copy of the file/s will remain in the original location, so you will need to take further action and can remove/rename that.
Send it from the User Files section of the chest (select the file, right click, email to Alwil Software). It will be uploaded (not actually emailed) to avast when the next avast auto (or manual) update is done.
Yes the cookies are nothing to worry about, but let SAS deal with them. Looks like MBAM removed the file but not the folder so SAS has done for that.
