[rubenv]

Only gripe here, and it's not a devdocs problem per se, is that Firefox deletes the offline documentation if you haven't opened devdocs in a while.

Is there any way I can turn that off, preferably on a per-site setting?

[voytec]

This site's cookies seem to be issued for some 2 months. You can extend cookies' lifetime in Firefox globally and per-site but a cookie can (and in most cases should) be invalidated on the server side.