Saved credentials autofill for example.com but not for login.example.com. This is a narrower problem than a total system outage. The first useful clue is the contrast between the failed action and a related action that still works. Do not reinstall or reset unrelated components before identifying which boundary is failing.
What the symptom tells you
Inspect saved login website origin and whether form is inside a third-party iframe. This comparison matters because an apparently identical error can be caused by a setting, the path used to reach the feature, or a capability the current device does not support.
Record the exact browser version, affected website origin, extensions and active profile. Note whether the behavior started after a specific update, connection change or account change. Keep one control case unchanged while you test the affected scenario; that gives you a reliable before-and-after result.
Three likely causes and how to separate them
| Possible cause | Evidence to look for | What it means |
|---|---|---|
| Saved origin mismatch | Inspect saved login website origin and whether form is inside a third-party iframe. | The issue is likely to follow the exact feature state or configuration, rather than every device or document. |
| Field marked autocomplete=off or generated dynamically | Repeat the same action with one known-good control while keeping the other conditions constant. | A difference between two accounts, connections or modes identifies the component to inspect next. |
| Password extension interception | Compare page login frame origin and credential manager entries without exporting passwords into plain text. | This possibility needs more evidence and should not be treated as confirmed after a single failure. |
The rows are diagnostic hypotheses, not a guaranteed diagnosis. For example, saved origin mismatch can coexist with a second issue, but changing several settings at once makes it impossible to tell which correction helped.
Before making changes
Do not clear passwords, browsing profiles or security protections until a clean-profile comparison demonstrates that they are involved. Always verify the hostname before choosing a stored credential.
Fix the problem in a controlled order
- Reproduce the actual failure. Saved credentials autofill for example.com but not for login.example.com. Keep the test short and use non-sensitive data wherever practical.
- Check a working baseline. Inspect saved login website origin and whether form is inside a third-party iframe. Write down what worked, what did not, and the version or mode in each test.
- Examine the first explanation. Saved origin mismatch. Look for an obvious setting or hardware state that differs from the control.
- Rule out the second explanation. Field marked autocomplete=off or generated dynamically. Change only one reversible setting or comparison variable.
- Apply the targeted fix. Select the correct saved login entry manually and test with Firefox extensions disabled temporarily.
- Check the result immediately. Correct login fields populate only on intended trusted origins. If it fails, restore the last changed setting before trying a different route.
Solution A: the least disruptive correction
Select the correct saved login entry manually and test with Firefox extensions disabled temporarily. Focus on the first setting, route or mode that differs from the control case. If a setting is absent on the current model, OS build or app version, do not invent a hidden menu or assume the user has that feature.
Reproduce the original failure right after applying the correction. A success in an easier, unrelated test is not enough: the same browser version, affected website origin, extensions and active profile should now behave as intended. If the result is mixed, keep notes and avoid continuing with broader changes.
Step-by-Step Troubleshooting
Beginner: check the feature without deleting data. Advanced: identify the underlying dependency using controlled evidence.
Identify the symptom
Saved credentials autofill for example.com but not for login.example.com. Identify the exact failing action, affected device/app and the time the problem began. Keep a record rather than testing from memory.
Compare with a working case
Inspect saved login website origin and whether form is inside a third-party iframe. Use a harmless sample and repeat with the same account, network and settings when possible. Only change one variable.
Make the small correction
Select the correct saved login entry manually and test with Firefox extensions disabled temporarily. Pause if the available menu or capabilities differ from the instructions for your product.
Verify without losing data
Correct login fields populate only on intended trusted origins. Reopen or reconnect once when relevant. Keep the old setting recorded so it can be restored if the result is worse.
Prove the first failure boundary
Check whether saved origin mismatch. Compare the outcome with: Inspect saved login website origin and whether form is inside a third-party iframe. A failing control means the first hypothesis is not sufficient.
Inspect the secondary dependency
Investigate field marked autocomplete=off or generated dynamically. Record the model, versions and connection or account difference. Preserve the working baseline.
Use deeper diagnostics safely
Compare page login frame origin and credential manager entries without exporting passwords into plain text. If the third cause — password extension interception — is involved, prefer official documentation and supported diagnostic utilities.
Recheck and document rollback
Correct login fields populate only on intended trusted origins. Always verify the hostname before choosing a stored credential. If this verification fails, undo only the latest change and capture a privacy-safe support report.
Solution B: determine which component is responsible
Compare page login frame origin and credential manager entries without exporting passwords into plain text. Take observations before making further changes. When the test indicates that an administrator policy, carrier service, device firmware, platform restriction or subscription entitlement is responsible, follow that supported path instead of trying to circumvent it.
A useful escalation record contains four facts: the precise symptom, a control result, one targeted action taken, and the outcome. Provide the browser vendor or website owner with the failing origin, version and behavior of a clean reproduction, excluding authentication data.
Solution Checklist
Verify the repair
Pass condition: Correct login fields populate only on intended trusted origins. Repeat the test after one ordinary reopen, reconnection or restart only when the affected feature needs it. Also check that the known-good comparison still works; this helps detect a fix that merely moved the problem elsewhere.
If it still fails
Return to the original baseline and collect evidence for the third possibility: password extension interception. Compare page login frame origin and credential manager entries without exporting passwords into plain text. If the supported options are exhausted, stop before destructive resets and contact the appropriate vendor or service provider with redacted observations.
Prevent the same issue from returning
Keep a record of the working browser version, affected website origin, extensions and active profile. After a major app, OS, firmware or network change, repeat the same short control test before modifying several options. This makes a recurrence easier to trace and protects settings that were already correct.
FAQ
Why does a similar device or app still work?
The two cases may differ in browser version, affected website origin, extensions and active profile. Inspect saved login website origin and whether form is inside a third-party iframe. A successful comparison isolates a condition; it does not prove that the failing hardware is defective.
Should I factory reset or reinstall first?
No. Always verify the hostname before choosing a stored credential. Try the reversible saved origin mismatch check and targeted fix before any action that could erase local data or settings.
What information is useful for support?
Include the exact symptom, affected product and current version, the controlled comparison and whether this check passed: Correct login fields populate only on intended trusted origins. Exclude passwords, tokens, private messages and full account identifiers.
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