I tried to use the history tracking that comes with Reddit Gold for about a week and it was virtually useless. After browsing on my phone and two computers only like 1 in 10 of the links would correctly show up as purple on the other devices (even just PC to PC it didn't work).

Edit: I should mention I bought Reddit Gold just for this feature, so I was optimistic that it'd work.

As an alternative, you can set reddit to hide links that you have voted upon which does not require a reddit gold account.

> although really they should really be maintaining the visit history themselves, as they do with Reddit Gold users

Another HTTP request between me and the content I want. Another 1s of RTT (UMTS link)... No.

This can be done in parallel with JS, without using an HTTP redirect.

Nope, if you fire the AJAX request directly on the onclick event, chances are high it will not be submitted/processed before the browser navigates away...

You could to do opt in permissions similar to the permission request for location information or for chrome desktop notifications.