Surprises can be appropriate in many situations, but they are not welcome when user security, privacy, and control are at stake. Mozilla is committed to guarding these principles, and we feel that a policy should be adopted that explicitly details our stance on these issues in regard to add-on modifications. The text of our proposal is below.

Changes to default home page and search preferences, as well as settings of other installed add-ons, must be related to the core functionality of the add-on. If this relation can be established, you must adhere to the following requirements when making changes to these settings: The add-on description must clearly state what changes the add-on makes.

All changes must be ‘opt-in’, meaning the user must take non-default action to enact the change.

Uninstalling the add-on restores the user’s original settings if they were changed. These are minimum requirements and not a guarantee that your add-on will be approved.

We welcome all constructive feedback and comments on this proposal, preferably in the AMO Newsgroup.

Update: The No Surprises policy has now been officially adopted and has changed slightly since this blog post. Read the official policy for details.