Bug tracking systems are a vital part of software project management. It is a necessary means to ensure the smooth development of modern large-scale open source software and continuously improve software quality. Most open source software ecosystems currently use open bug tracking systems to manage software bugs. It allows users to submit system failures (called defect bugs) and suggestions for system improvements (called enhancement bugs), but the role of feedback from these users has not been fully studied. Therefore, this work conducted an empirical study on the bug tracking system used by Firefox, and collected 19 474 and 3 057 bug reports submitted in 2018 and 2019 for Firefox Desktop and Firefox for Android, respectively. Based on this, it is compared and analyzed the differences between the number, severity, distribution on components, fixing rate, fixing efficiency and assignees of bugs submitted by ordinary users and core developers, and at the same time, the relationship between the quality of bug reports and the fixing rate and efficiency of bugs is investigated. The main findings are as follows. (1) There are a large number of ordinary users, but their participation is still superficial. 86% of ordinary users have only submitted one bug and no more than 3% of bugs are of high severity. (2) The bugs submitted by ordinary users mainly distributed on UI components related to user interaction (e.g., address bar, audio/video, etc.), but there are also 43% of bugs that are difficult to accurately locate due to lack of sufficient description information. (3) In terms of bug processing results, due to the simple design of the duplicate checking system and bug filling system, a large number of bugs are treated as "useless" ones, and the fixing rate is less than 10%. (4) In the bug fixing process, due to the difficulty of ordinary users to accurately and fully describe bugs, the system does not pay enough attention to them, thus the process of bugs submitted by ordinary users is more complicated than that of core developers, and it takes at least 8 more days on average to fix them. These results reveal the shortcomings of the current bug tracking system in terms of user participation incentive mechanism, automatic bug duplicate checking, and intelligent assistance in filling out bug reports, which can provide help for the system developers and managers to improve system and enhance the contributions of ordinary users to open source software.