Firefox users and session loss bug/en

If you see the error message below, and you are using the Firefox browser, then it might be because of a known browser bug. The steps to fix it, are below.

The same problem with the SeaMonkey (Mozilla) browser can be fixed the same way, only remember to restart your browser afterwards.

Firefox 71+
You might need to reload the page, or re-log-in, or restart your browser, for the fix to start working. But probably not.
 * 1) Open a new tab or window
 * 2) type or paste   in the address bar, and click "Enter". (There might be a warning screen after this. Continue only if you are an experienced user)
 * 3) type or paste   in the search bar
 * 4) if the preference exists, click the pencil icon to edit it. Otherwise select "Number" and click the plus icon
 * 5) enter a value (see below), and click the tick icon to save

Firefox 70 and lower
You might need to reload the page, or re-log-in, or restart your browser, for the fix to start working. But probably not.
 * 1) Open a new tab or window
 * 2) type or paste   in the address bar, and click "Enter". (There might be a warning screen after this. Continue only if you are an experienced user)
 * 3) right-click anywhere in the table of results (pay attention not to alter the existing data)
 * 4) select "New"
 * 5) select "Integer"
 * 6) type or paste   as the preference name, and click "OK"
 * 7) type a value (see below), and click "OK"

Value: any number between 200 and 2000 should work fine. Estimate 5+ cookies per wiki, and only count the project (e.g. Wiktionary) that you access the most languages of.

Further information

 * T151770
 * https://bugzilla.mozilla.org/show_bug.cgi?id=1319403