  Fixing bugs is an important phase in software development and maintenance. In
practice, the process of bug fixing may conflict with the release schedule.
Such confliction leads to a trade-off between software quality and release
schedule, which is known as the technical debt metaphor. In this article, we
propose the concept of debt-prone bugs to model the technical debt in software
maintenance. We identify three types of debt-prone bugs, namely tag bugs,
reopened bugs, and duplicate bugs. A case study on Mozilla is conducted to
examine the impact of debt-prone bugs in software products. We investigate the
correlation between debt-prone bugs and the product quality. For a product
under development, we build prediction models based on historical products to
predict the time cost of fixing bugs. The result shows that identifying
debt-prone bugs can assist in monitoring and improving software quality.
