Each bug in Bugzilla keeps track of changes made to it. You can view these changes by clicking the History link at the top right of the page.
The obvious question is “what gets tracked?”
The answer is “a lot, but not everything”
Specifically these fields are tracked:
- product
- qa_contact
- assigned_to
- keywords
- time tracking
- comment privacy
- component
- cc
- alias
- keywords
- dependson
- blocked
- group
- see_also
- flags
- duplicates
- custom fields
Unfortunately descriptions and comments are not tracked.