Similar to Bug 1629226, it is likely that much of the Form Manager does not work when login forms are in a Shadow DOM.

I encountered one example of this while working on Bug 1643163, where the Form History autocomplete popup does not show when the username field is in its own Shadow Root. My best guess is that the Form Manager is not finding the <form> element in this situation.

STR
In a test profile for toolkit/components/passwordmgr/test/browser/form_basic.html:

1. Load the page in a HTTPS context.

• I set up a local HTTPS Apache server to achieve this.

2. Delete any logins for the site via about:logins.
3. Enter in a fake username value and click the Submit Query button. After the form is submitted, the page should reload with an empty username field.
4. Focus on the username field.
5. Observe the Form History autocomplete popup, with the username value previously entered as an option.
6. Repeat steps 1-4 in the same profile with toolkit/components/passwordmgr/test/mochitest/form_basic_shadow_DOM_each_field_in_its_own_shadow_root.html (from Bug 1638587).
7. Observe that upon focusing the username field, there is no Form History autocomplete popup shown.

Expected results
There is a Form History autocomplete popup for the form_basic_shadow_DOM_each_field_in_its_own_shadow_root.html page.

Actual results
There is no Form History autocomplete popup for the form_basic_shadow_DOM_each_field_in_its_own_shadow_root.html page.

Logs
Attached are the logs generated from these STR by running Firefox with MOZ_LOG="satchel:5" for C++ logging and setting browser.formfill.debug to true in about:config for JS logging.

Thanks! Looks like it's saving at least:

satchelFormListener: sending entries to parent process for form form-basic

I'm a bit confused about the regressing bug here - what versions are affected based on that dependency?

We shipped Shadom DOM in Fx63 according to https://caniuse.com/#feat=shadowdomv1