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If you use the Subreddit chooser to manually enter a name that doesn't appear on the default list, that entry seems to stay there forever even if you log out and switch accounts. This creates a potentially embarrassing information leak e.g. if you have an account for NSFW subreddits.
As a separate issue, there doesn't seem to be an option to clear this list? It isn't cleared with the "clear browsing history" button.
Confirmed feature request. Thanks.