Features:
• Tell at a glance if a fic was unseen, skipped or seen by @Min_'s AO3: Kudosed and seen history or my KHX script.
• Also indicate ⧉ Series links (not seen-able) to prevent confusion.
• Live highlights update on back-forward navigation and focus after state changes.
• Low overhead, exits if there are no links on the page.
• Notification and Backup download if 30+ works suddenly disappear (your cookies probably got deleted!).
note: Author links and direct chapter links cannot be highlighted.

This feature was added to match my other script AH/DLP/QQ/SB/SV/FFN/HPF/PC/OR Highlight visited fanfics's reddit highlighting capability, but for AO3 and @Min_'s data storage.
I was going to add the feature to KHX for "AO3: Kudosed and seen history", but I wanted to try making a more lightweight script that could run on every subreddit, so I ended up making it compatible with both scripts.
Seen/skipped updates are passively intercepted on AO3 and copied to private GM storage to share across Reddit (this reuses my HVF's cache-safe storage --no corruption-- designed for real-time updates, with back-forward navigation and alt-tab.)
It is designed to quickly abort itself if no links are found on the page making it very efficient.
Still, if you'd like to restrict it to a few subreddits, edit the commented @include
atop the code (you may want to disable updates to preserve that edit.)
Note: New Reddit cannot be supported due to links loading dynamically.
Backup feature: Since the script has a private copy of your seen/skipped data, it can detect loss from cleared cookies. The loss detection threshold is 30 entries disappearing at once; if you have more than that, your data will be protected. The message is:

