How do you keep track of papers during a brainstorming literature review?
My workflow/suggestion would be to keep this all in Zotero. I'm a big believer in keeping the number of tools one uses relatively small and becoming very proficient at using ones favorite tools.
I use a collection  ("Inbox") dedicated to items I may or may not keep and don't have time to read right away. I will then go through those items periodically and either throw them out (remember you need to "Move to trash" or shift+delete - just pressing delete will just delete them from the collection.) or file them in the right collection and delete them from "Inbox". 
To quickly remind you of why you saved the items, you could either attach Zotero notes or you could use tags, including colored tags if you can make do with only a couple of short keywords. 
Finally, since you will always save items into Zotero right away, you can sort the collection by "date added," which should give you a good idea of the context in which you saved an item.
Since you're using Zotero Standalone, you'll want to use alt+tab to quickly move back and forth between Zotero and your browser.