You can use %i macro, which is effectively the same as redirection to /dev/null.
If those :file entries come from your vifmrc file, you can just add %i there. If they are from some .desktop-file, you can press c on an entry and then edit the command by appending %i.
However the program's output is not suppressed which is really needed for most programs.
It depends on programs you use. If they are terminal-based, ignoring their output by default can break them and there is no way for vifm to know if particular application is running in terminal or has a GUI. So showing errors by default seems to be the safest and universal choice.