When two small bubbles approach each other, a dimpled thin liquid film is formed between them. A model is developed for the dynamics of the thinning film with mobile interfaces, in which the effects of surface tension gradient and surface viscosities upon the surface mobility, drainage, and rupture of a dimpled liquid film are investigated. The model predicts the coalescence time, which is the time required for the thinning and rupture of the liquid film, given only the radii of bubbles and the required physical properties of the liquid and interfaces, such as surface tension and surface viscosities, London-van der Waals constant, and surface diffusion coefficient. The predicted result is in good agreement with previous experimental results.