The little riveted points you mention are pivots, there are a bunch of them. What you can do is spray a little lubricant in each pivoting part of the derailleur, then physically move it side to side by hand a number of times and it should loosen up. Pull it towards you and then push it back, 10, 20, 30 times.
It might take a bit of force to start with and additional lubricant into the moving surfaces will flush out the dirt. Front derailleurs are quite simple mechanisms so a) you shouldn't damage it and b) if this doesn't get it moving then it is probably past it.
I've seen this numerous times with old/dirty and in particular, underused derailleurs. if someone has a triple chainset but doesn't use the smallest ring, for example, then the FD can easily seize up in time.