help: update preferences navigation to v40
Closes #1263 (closed)
I set the pkgversion to 40.alpha. I don't know if .alpha is really useful. Perhaps it could be a reminder to double-check if the pages are still valid before v40 release?
I marked pref-cookies.page
as outdated and did not make any correction except for the preferences path. I think it should be fixed in another MR.