This article reports on a study which took place in the context of the design and development of an online dictionary prototype for learners of French. Aspects of the "usability", i.e. the quality of the "learner-task-dictionary interaction" of the prototype were tested. Micro-tasks were designed to focus on learners' productive knowledge of French collocations. Learners (n = 6) completed the tasks individually, with access to the dictionary prototype. The computer sessions were screen-captured. The product (the language input provided by the learners) and the process (the learners' behavior) of the interaction were analyzed based on a set of defined effectiveness and efficiency parameters. The results provide an insight into the learners' dictionary search and look-up strategies highlight areas of the prototype's interface that deserve further design attention and consolidate the methodology used to test the usability of the prototype. (Contains 8 figures, 3 tables and 2 notes.)