An international firm refer to the firms headquartered in United States who make sizable investments outside the United States with multiple profit centers.
A profit center is a unit or department of an organization that incurs costs and generates revenues.
In the given case, Mars, the large candy company has it's headquarters at McLean, Virginia, but has many divisions and operations spread across the world in different countries. Thus, Mars represents an international firm whose investments are spread across different nations with multiple profit centers.
Numerous number of consumers or buyers protects a firm from being forced to sell its products at an unfairly low price. This is one of the important reasons that a firm can sell its product at a good price. If the competition increases, then the firm has to beat the competition to get the required price, otherwise it might have to lower its price to hold on to its consumers.