I sorted out a problem with a friend's computer today and she used the now time-honoured phrase "This stupid computer."
Reflexively I repeated the mantra "Computers are stupid so we have to be clever." which is one of those "things teachers say."
My daughter plays the flute. Imagine a recalcitrant pupil picking up a flute and finding he or she can't get a beautiful tune out of it immediately. "'ere this flute don't work" "this flute is crap!"
Another "thing teachers say" (or at least this teacher) is "imagine you are playing a computer game. You would not sit waiting for a teacher to come and show you what to do, you would experiment. Treat Mozilla the same way, try things out, experiment, see what happens. There is an "undo" button if it goes wrong. You cannot damage the program or the computer unless you are a total pilchard."
Yesterday was a good day at work. Two unpromising classes responded very well and got stuck in with Mozilla. The "learned helplessness" was in abayance. It will be interesting to see if the same thing happens with spreadsheets after half term :)