afaik LMDE comes with some non-free stuff preinstalled, in Debian and siduction you would have to enable non-free in the sources.lists.
If your wifi is one that needs non-free firmware, you have to use (wired) ethernet to enable and install the needed package(s) once, the installer offers to add non-free for you.
I don't know your model, so I can't say if you just need some non-free firmware or if your chip isn't supported at all, but I am pretty sure it is, if it can be used with LMDE.