Force subreddits to use the default theme, even while logged out
Its main use is to allow a custom userstyle that's consistent across all of reddit, without having to fight with each subreddit's custom theme...especially when logged out.
Besides removing custom themes, it also restores the snoo alien mascot in the header that some subreddits replace, and it removes the huge "signup" banner when viewing comment pages.
Note: This script is not for the new (beta) Reddit redesign which became available around April or May of 2018. You'll need to go to old.reddit.com to restore the old design, and then this script should work.
Note2: Users of uBlock Origin (on Firefox 57+) may want to use the following static filter instead of my userscript:
reddit.com##^link[title="applied_subreddit_stylesheet"] reddit.com###header-img reddit.com##.listingsignupbar
