Did you check the Downloads window? { Ctrl + J }

yes i did, anyways, when u download add-ons theres no trace whatso ever of their downloading. or is there?

Sorry, I was wrong. I was looking at a Downloads window in a Profile that I had used to download & save some extensions, rather than installing those extensions directly from the AMO website. I just directly installed an extension, and NO it didn't appear in the Downloads window.

The only other thing that I can think of is to do a search of your browsing History - {Crtl + Shft + H} upper-right corner of that window = Search History - for addons and look thru that search list.