Default Screen Choice - Advange Target for DMA is not working

[data-sync-user]

We have an advance target configured in this experiment https://experimenter.services.mozilla.com/nimbus/ios-dma-remove-set-to-default/summary/. But if you see the experiment if only enrolled 100 user so far. We have around 1000 new users per day coming from DMA.

What the target does?

• If you are coming from the DMA screen, we exclude the onboarding default browser card, so the user doesn’t need to see that again.

┆Issue is synchronized with this Jira Bug

[data-sync-user]

➤ Laurie Marceau commented:

I had commented on Slack about this issue here ( https://mozilla.slack.com/archives/C05C9RET70F/p1758552700522759 ):

{quote}We collect some telemetry for the choiceScreenAcquisition and indeed the numbers don't match ( https://mozilla.cloud.looker.com/explore/firefox_ios/metrics?qid=zFEkWSpLbAzFUxGiaAqMo0&toggle=vis )

I double checked we are calling the default browser Apple API ( https://developer.apple.com/documentation/uikit/uiapplication/isdefault(_:) )  before we setup the nimbus experiments. We're also saving/fetching that information in the proper place (both the save/retrieve is done with the UserDefaults.standard . So the experiment should have the right information to work.
TLDR; I didn't see the problem yet.{quote}

[data-sync-user]

➤ Laurie Marceau commented:

Looking at Nimbus documentation, I posted here ( https://mozilla.slack.com/archives/CF94YGE03/p1758555172517499 ) to ask some questions:

{quote}Hello! I am trying to understand the Expected enrolled clients number we set on experiments. Does it have effect on enrolled population count? 

The documentation ( https://experimenter.info/validating-experiments/#low-enrollments ) seems to point to yes, but the experience from the team is that it doesn't? I am just trying to understand if that number is important when we setup experiments{quote}

jlockhart answered:

{quote}It doesn't affect the clients in any way, it's used as a reference so that later when someone looks at the enrollment dashboard, if the number of actually enrolled clients is wildly off from the expected enrolled clients, that's an indication that something has gone wrong{quote}

[data-sync-user]

➤ Laurie Marceau commented:

The documentation states low enrolments could be (striking-through for options we have investigated):

• An error in sizing calculations (your expected count was off)
• The experiment conflicts with other experiments or rollouts targeting the same feature-
• Misconfiguration in experimenter (e.g. you selected the wrong release version or channel)
• A bug in server-side targeting expressions
• A bug, timeout, or implementation error in client-side targeting attributes;
• You launched the experiment during the first week of a new release, during which actual users are still updating to the latest version of Firefox

[data-sync-user]

➤ Laurie Marceau commented:

(is_default_browser == true && is_first_run) && (app_version|versionCompare('138.1.0') >= 0) is the targeting expression of that experiment.

• is_default_browser should work as expected
• is_first_run should work as expected
• app_versionshould work as expected

[data-sync-user]

➤ Laurie Marceau commented:

Issam found out the issue might be caused by those unmerged changes: #29450 ( https://github.com/mozilla-mobile/firefox-ios/pull/29450|smart-link ) The PR was merged and it’s targeting 144.1, so once that ships the problem hopefully is resolved

[data-sync-user]

➤ Issam Mani commented:

For future reference if anyone needs to debug enrollment status or jexl evaluations.

• Use a local AS build on iOS ( by running this script ( Build FXIOS-13790 [AS] Add script to automate building and comsuming a local AS build #29868 ))

• Trick Nimbus into thinking you are on the channel that your experiment is targeting.
  In this case ios-dma-remove-set-to-default was targeting release so I had to change these lines (

  firefox-ios/MozillaRustComponents/Sources/FocusRustComponentsWrapper/Nimbus/NimbusCreate.swift

  Lines 138 to 139 in c5ff632

  	appId: info["CFBundleIdentifier"] as? String ?? "unknown",
  	channel: appSettings.channel,

  ) to reflect that:
  appId: "org.mozilla.ios.Firefox",
  channel: "release",

• In order to see the enrollment status of an experiment, I added an info! inside evolve_enrollments_in_db ( https://github.com/mozilla/application-services/blob/1d1096c3a3c8eb039a7e07d8aedd3dbe8c16f471/components/nimbus/src/stateful/enrollment.rs#L25 ) after this line ( https://github.com/mozilla/application-services/blob/1d1096c3a3c8eb039a7e07d8aedd3dbe8c16f471/components/nimbus/src/stateful/enrollment.rs#L45 ) to print all change events.
  for ev in &enrollments_change_events {
  info!(
  "[dbg][issam] change slug={} type={:?} branch={:?} reason={:?}",
  ev.experiment_slug, ev.change, ev.branch_slug, ev.reason
  );
  }

• The output was:
  💙 INFO[sync] RustErrors - [dbg][issam] change slug = ios - dma - remove - set - to -default type = EnrollFailed branch = "N/A" reason = Some("feature-conflict")
  This hinted that it was conflicting with another experiment. The only other experiment targeting the same feature was ios-dma-onboarding

• Removing ios-dma-onboarding from the initial_experiments.jsonfile and logging the same change events resulted in the experiment attempting to enroll but not enrolled because the target didn’t eval to true.

• Next, just to make sure it all works, I did a sanity check on the jexl targeting string. By adding this code to eval_jexl ( https://github.com/mozilla/application-services/blob/1d1096c3a3c8eb039a7e07d8aedd3dbe8c16f471/components/nimbus/src/targeting.rs#L48 ), I was able to see the context, targeting string and result of the evaluation
  ...
  info!("[dbg][issam] eval_jexl expr {:?}", expr);
  info!("[dbg][issam] eval_jexl context {:?}", self.context);
  ....
  let foo = jexl_eval(&expr, &self.context, self.event_store.clone(), self.gecko_pref_store.clone());
  info!("[dbg][issam] eval_jexl result {:?} {:?}", expr, foo);
  return foo;
  ...

• At first the target evaluated to false ( Notice the result line says Ok(false)) because is_default_browser is false. So targeting works as expected in this case.
  2025-10-07 21:04:13.910 💙 INFO [sync] RustErrors -
  [dbg][issam]
  eval_jexl expr
  "(is_default_browser == true && is_first_run) && (app_version|versionCompare('138.1.0') >= 0) && (region in ['AU', 'BE', 'BG', 'CY', 'CZ', 'DE', 'DK', 'EE', 'ES', 'FI', 'FR', 'GR', 'HR', 'HU', 'IE', 'IT', 'LT', 'LU', 'LV', 'MT', 'NL', 'PL', 'PT', 'RO', 'SE', 'SI', 'SK'])" - target: nimbus::targeting
  2025-10-07 21:04:13.910 💙 INFO [sync] RustErrors -
  [dbg][issam]
  eval_jexl context
  Object {"active_experiments": Array [], "android_sdk_version": Null, "app_build": String("1"), "app_id": String("org.mozilla.ios.Firefox"), "app_name": String("firefox_ios"), "app_version": String("144.1"), "architecture": String("Mac16,8"), "cannot_use_apple_intelligence": Bool(false), "channel": String("release"), "current_date": Number(1759863853), "days_since_install": Number(0), "days_since_update": Number(0), "debug_tag": String("Nimbus.rs"), "device_manufacturer": String("Apple"), "device_model": String("arm64"), "enrollments": Array [], "enrollments_map": Object {}, "events": Object {"days_opened_in_last_28": Number(0)}, "has_accepted_terms_of_use": Bool(false), "has_enabled_tips_notifications": Bool(false), "home_directory": Null, "installation_date": Number(1759863845660), "isFirstRun": String("true"), "is_already_enrolled": Bool(false), "is_apple_intelligence_available": Bool(true), "is_bottom_toolbar_user": Bool(false), "is_default_browser": Bool(false), "is_first_run": Bool(true), "is_phone": Bool(true), "language": String("en"), "locale": String("en-DE"), "nimbus_id": String("d49f46e4-c7eb-4c4f-8c6c-f83b57983bf7"), "os": String("iOS"), "os_version": String("26.0"), "region": String("DE")} - target: nimbus::targeting
  2025-10-07 21:04:13.911 💙 INFO [sync] RustErrors -
  [dbg][issam]
  eval_jexl result
  "(is_default_browser == true && is_first_run) && (app_version|versionCompare('138.1.0') >= 0) && (region in ['AU', 'BE', 'BG', 'CY', 'CZ', 'DE', 'DK', 'EE', 'ES', 'FI', 'FR', 'GR', 'HR', 'HU', 'IE', 'IT', 'LT', 'LU', 'LV', 'MT', 'NL', 'PL', 'PT', 'RO', 'SE', 'SI', 'SK'])" Ok(false) - target: nimbus::targeting

• For completness, I set is_default_browser to true here (

  firefox-ios/firefox-ios/Client/Experiments/RecordedNimbusContext.swift

  Line 197 in c5ff632

  "is_default_browser": isDefaultBrowser,

  ) to mimic user setting firefox as the default browser in the choice screen. Logging the same info for the target shows that the user is enrolled and that the target string evaluated to true this time.
  2025-10-07 21:15:22.932 💙 INFO [sync] RustErrors -
  [dbg][issam]
  eval_jexl expr
  "(is_default_browser == true && is_first_run) && (app_version|versionCompare('138.1.0') >= 0) && (region in ['AU', 'BE', 'BG', 'CY', 'CZ', 'DE', 'DK', 'EE', 'ES', 'FI', 'FR', 'GR', 'HR', 'HU', 'IE', 'IT', 'LT', 'LU', 'LV', 'MT', 'NL', 'PL', 'PT', 'RO', 'SE', 'SI', 'SK'])" - target: nimbus::targeting
  2025-10-07 21:15:22.932 💙 INFO [sync] RustErrors -
  [dbg][issam]
  eval_jexl context
  Object {"active_experiments": Array [], "android_sdk_version": Null, "app_build": String("1"), "app_id": String("org.mozilla.ios.Firefox"), "app_name": String("firefox_ios"), "app_version": String("144.1"), "architecture": String("Mac16,8"), "cannot_use_apple_intelligence": Bool(false), "channel": String("release"), "current_date": Number(1759864522), "days_since_install": Number(0), "days_since_update": Number(0), "debug_tag": String("Nimbus.rs"), "device_manufacturer": String("Apple"), "device_model": String("arm64"), "enrollments": Array [], "enrollments_map": Object {}, "events": Object {"days_opened_in_last_28": Number(0)}, "has_accepted_terms_of_use": Bool(false), "has_enabled_tips_notifications": Bool(false), "home_directory": Null, "installation_date": Number(1759864517814), "isFirstRun": String("true"), "is_already_enrolled": Bool(false), "is_apple_intelligence_available": Bool(true), "is_bottom_toolbar_user": Bool(false), "is_default_browser": Bool(true), "is_first_run": Bool(true), "is_phone": Bool(true), "language": String("en"), "locale": String("en-DE"), "nimbus_id": String("663fdfa2-70ba-4af1-b698-d0766fc18b10"), "os": String("iOS"), "os_version": String("26.0"), "region": String("DE")} - target: nimbus::targeting
  2025-10-07 21:15:22.932 💙 INFO [sync] RustErrors -
  [dbg][issam]
  eval_jexl result
  "(is_default_browser == true && is_first_run) && (app_version|versionCompare('138.1.0') >= 0) && (region in ['AU', 'BE', 'BG', 'CY', 'CZ', 'DE', 'DK', 'EE', 'ES', 'FI', 'FR', 'GR', 'HR', 'HU', 'IE', 'IT', 'LT', 'LU', 'LV', 'MT', 'NL', 'PL', 'PT', 'RO', 'SE', 'SI', 'SK'])" Ok(true) - target: nimbus::targeting