Mozilla (Firefox)

Mozilla’s Bugzilla is the original public bug tracker, and one of the longest-running examples of a software project surfacing its known issues to the public. Firefox plus all Mozilla projects (Thunderbird, Servo while it existed, etc.) use it as the canonical issue surface.

The historical depth is worth noting on its own: bugs filed in the late 1990s still cross-reference newer issues, which makes the tracker a real archive of web-platform evolution. For practical use, the per-product filters are how you narrow to whatever you care about.