Some of the prefs specific to TAAR v3 remain displayed in "about:config" page after the add-on is uninstalled

[SoftVision-CarmenFat]

[Affected versions]:

• Firefox 61.0

[Affected Platforms]:

• All Windows
• All Linux
• All Mac

[Prerequisites]:

• Have a new Firefox profile with the latest version of the "TAAR v3" add-on (downloaded from https://bugzilla.mozilla.org/show_bug.cgi?id=1469546) installed.
• Create the following prefs in the "about:config" page: "shieldStudy.logLevel" as string and set it to "All"; "extensions.taarexpv3_shield_mozilla_org.test.variationName" as string and set it to "control", "intervention-a" or "intervention-b"

[Steps to reproduce]:

1. Open the browser with the profile from prerequisites and navigate to "about:addons" page.
2. Click the "Extensions" section from the left side of the page.
3. Click the "Remove" button specific to the TAAR v3 experiment.
4. Go to "about:config" page and observe if any prefs remained displayed related to the experiment.

[Expected result]:

• The prefs related to the TAAR v3 experiment are no longer displayed.

[Actual result]:

• Some prefs related to TAAR v3 are still displayed: -> browser.pageActions.persistedActions -> extensions.taarexpv3_shield_mozilla_org.client-status -> extensions.taarexpv3_shield_mozilla_org.test.variationName -> extensions.webservice.discoverURL

[Notes]:

• Attached a screen recording of the issue:

[motin]

These should indeed be removed: -> extensions.taarexpv3_shield_mozilla_org.client-status -> extensions.taarexpv3_shield_mozilla_org.test.variationName

These two prefs are native to firefox and should not be removed: -> browser.pageActions.persistedActions -> extensions.webservice.discoverURL

@SoftVision-CarmenFat, @mlopatka: Would it be enough if we track the original preference values at the start of the study and then reset these prefs to their original values at the end of the study?

[mlopatka]

@mlopatka: Would it be enough if we track the original preference values at the start of the study and then reset these prefs to their original values at the end of the study?

For me, this would be the expected and correct behaviour.

[motin]

@SoftVision-CarmenFat: In the develop branch (yet to be released and signed), the add-on now restores extensions.webservice.discoverURL to its original values (pre-study) at the end of the study. The browser.pageActions.persistedActions pref gets modified as a side-effect and should not be restored to it's original value. Instead, the add-on now removes the add-on references from it's .ids and .idsInUrlbar properties.

Note however that until https://github.com/mozilla/shield-studies-addon-utils/issues/232 is resolved, we can only expect cleanup to run upon expiration of the add-on, and not when the user/normandy uninstalls/disables the add-on.

[Softvision-MariusComan]

This issue is no longer reproducible with the latest version of the "TAAR v3" add-on (3.0.2) installed on latest Firefox release (61.0.1) and latest Firefox Beta (62.0b7). Verified on Windows 10 x64, Mac 10.13 and Arch Linux. Now the prefs are reset to their original values after the add-on expires. We will also retest the user disable/remove scenarios after fixing 232, therefore this report will remain open for the moment.

[motin]

Quick update: issue 232 in utils has been closed in favor of https://github.com/mozilla/shield-studies-addon-utils/issues/246