Defect Severity


We use the severity field in Bugzilla to indicate the scope of a bug’s effect on Firefox.

The field is display alongside the bug’s priority.

Screenshot of severity field


Severities are enumerated as:

  • --: Default for new bugs

  • N/A: (not applicable): Only applies to bugs of type Task or Enhancement.

  • S1: (Catastrophic) Blocks development/testing, may impact more than 25%

    of users, causes data loss, potential chemspill, and no workaround available

  • S2: (Serious) Major Functionality/product severely impaired and a

    satisfactory workaround doesn’t exist

  • S3: (Normal) Blocks non-critical functionality and a work around exists

  • S4: (Small/Trivial) minor significance, cosmetic issues, low or no impact to users

By default, new bugs have a severity of --.

Rules of thumb

  • A crash may be be a ``S1`` or ``S2`` defect, but not all crashes are critical defects

  • If a bug’s severity is S1 or S2 then it must have an assignee

  • The severity of most bugs of type task and enhancement will be N/A

  • Do not assign bugs of type defect the severity N/A