Hello,
Whether terminal multiplexer support is active or not can be saved in vifminfo file, but for that your 'vifminfo' option should contain state value. You can add it in your vifmrc like this:
set vifminfo+=state
It will also save state of filters, so if you don't want that and 'vifminfo' does not contain state just put
screen
directly to your vifmrc.
Note that you don't want to combine state with screen because :screen in vifmrc toggles support (related issue). Next version (after 0.8.2) will include :screen! form which always enables the support instead of toggling it, that one can be put into vifmrc without odd behaviour every other time vifm is run.