=== Dealing with regressions ===
For some bugs the reporters will tell you that something used to work and doesn't work anymore. These are called regressions. (But first, make sure that it's really only the Thunderbird build that's different between "works" and "doesn't work", and the reporter didn't change 15 other things between testing the new and old Thunderbird build
- if he did, that would create major confusion and waste lots of developer time).
If it's a real regression, flag these bugs with the "regression" keyword, and then find a regression range. This can be easily found using our [[Thunderbird:Testing/Regression regression instructions]].