Benzotriazole, phenyl mercapto tetrazole and nitro-benzimidazole nitrate are all classed as antifoggants in photo engineering usage. They adsorb to the crystal surface and form mild to strong salt like materials or complexes with the silver halide to reduce development rate and fog formation. These complexes are much less soluable than the original silver halide itself. While doing so, they also 'tone' the image changing the color of the silver metal by changing the form taken by developing silver metal.
Bromide is one of the constituents of a grain in many cases and retards development simply by changing solubility of silver halide or by a counter ion effect. Development produces halide. If you add enough of the halide to the developer to start with, development slows down. Fog slows down, speed slows down and contrast lowers. Of course, this is often the same result as the antifoggants I list, but by a slightly different method. It also requires different amounts of each of these to get to approximately the same point.
Thanks for this very lucid and complete explanation. It is very helpful and interesting.