In T85923#2429254, @Tgr wrote:

In T85923#2428390, @Ikaruseijin wrote:

According to what I have done the number is "2600025."

Thanks! Can you also check what number this website gives (in the "Results will appear below" section)?

In T85923#958482, @Tgr wrote:

I don't use Safari myself but googling it says that you can open the console with Option+Cmd+C. After that just copy/paste encodeURIComponent(JSON.stringify(localStorage)).length in the window that opened and press enter.

In T85923#958186, @Tgr wrote:

Thanks for taking the time to report this!

I always use https: connections, never anything else.

I presume you always use the same domain as well? There is no way to make browsers store data for multiple domains, so if you disable on en.wikipedia.org and go to de.wikipedia.org, you have to disable again - that's a security limitation that we have no realistic way of circumventing.

Apart from that, the settings should stick forever. They use localStorage, not cookies - the two mostly behave the same, but there are a few differences. A few things two check:

• please test your localStorage quota here and how much space is used by running encodeURIComponent(JSON.stringify(localStorage)).length. Theoretically running out of space should not cause anything like this (setting a value in localStorage should either fail immediately or last indefinitely) but still worth checking.
• do you see any pattern in when the settings are lost? Does it correlate to the deploy cycle? MediaWiki uses localStorage to cache javascript files, maybe that pushes other content out somehow (although again that should not happen).
• please try to set something unrelated to MediaViewer in localstorage and see if it shows the same behavior. The easiest way is to enable web font downloading in the language selector and seeing if it sticks for several weeks. (According to the spec User agents should expire data from the local storage areas only for security reasons or when requested to do so by the user. Most browsers do that, but mobile Safari is known to ignore the spec in some cases, especially if it is running out of disk space. I haven't found anything definite about desktop Safari.)

No I am not logged in most times, I only made an account to complain about the Media Viewer, so I have no need to be.