Factual error: At the beginning of the movie when Salieri is first talking to the priest asking him if he recognizes some of his songs, they cut away to an opera. A woman can be seen descending stairs where there appears to be smoke falling down the stairs, which would have to be dry ice. While it was first discovered/observed in 1825, it wasn't commercially available until 1925.
Continuity mistake: In the extended version of the DVD, there's a scene where Constanza goes to sleep with Salieri. In one shot there's a very prominent candle next to or just behind her on her right that smoking like it's just been extinguished. But from the front view there are no candles that close to her, and the ones a short distance away are all lit.
Factual error: In the scene where Constanza starts to undress in Salieri's rooms, it is revealed she is wearing a 1980s style strapless bustier with separate bust cups and lots of frothy lace. This is not historically accurate. Women wore corsets which shaped their torso into a conical shape, pushed the bust together and up, and they generally had shoulder straps. The corsets were also mostly unembellished, so as to keep a neat silhouette under tightly fitted dresses.
Continuity mistake: When Salieri has brought Mozart to bed and they are talking, Salieri is holding the candlestick. In the different views - from Mozart's and Salieri's - it can be seen that the angle he holds the candles changes. The line between the candles changesi. So Saleri held the candlestick in another angle the second time the scene was shot.
Visible crew/equipment: When Mozart and family visit a parody on several operas of his in a public theater, in one part of the show little people appear from all sides of the stage. When the last of the little people (carrying a model of horse) hops through a paper wall on the side of the stage, you can see a man in jeans walking behind the set.
Visible crew/equipment: Mozart is composing The Requiem Mass when Constanze admits a late-night caller. The door she opens reflects a large, bright square of light that looks like a sun-lit window (only it's night) - or more likely, a studio reflector. (It's definitely not the burning candles. Wrong shape.).