User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:60.0) Gecko/20100101 Firefox/60.0
Steps to reproduce:
- Enable permanent private browsing mode and restart Firefox.
- Go to https://www.twitch.tv and open any stream.
- Adjust some settings on the site like setting the video quality to the source and confirming that you are an adult (if the stream asks you that).
- Close all tabs/windows for the host twitch.tv.
- Wait a bit (usually between 0 and 15 seconds).
- Go again to https://www.twitch.tv and open any stream.
Settings like the selected video quality and confirming that you are an adult are reset.
The settings should still have been saved.
I noticed this issue first when I switched to permanent private browsing mode on Linux some months ago. This issue also persisted after switching to Windows 10.
I'm also a bit curious that this data is not deleted as long as one site for Twitch is kept open and that it needs usually a few seconds after the data is deleted when all sites for Twitch are closed. I guess the data gets deleted once Firefox finished unloaded the sites from its content process.
https://support.mozilla.org/en-US/kb/private-browsing-use-firefox-without-history documents that for example cookies should be cleared at the end of the session and not after all sites of a host are closed. This documented behavior is observed on any other websites that I noticed so far (like YouTube) and Twitch is the only site that I have seen so far breaking here.