Bugzilla

**Note**
* After saving the credentials by logging into the website, when returning to the login page, only the password is being auto-filled, not the email, also.

**Affected versions**
* Nightly v68.0a1
* Beta v67.0b5
* Release v66.0.2

**Affected platforms**
* Windows 10
* Mac OS 10.13.6
* Ubuntu 16.04

**Steps to reproduce**
1. Open Firefox with a new profile.
2. Reach: https://www.sogou.com/
3. Click on the orange "登录" (login) button from the top-right corner of the screen.
4. Click on the "帐号密码登录" link, the left of the 3 links under the QR code.
5. Input any mail and password inside the input boxes.
6. Click the "Sign In" button.
7. A pop-up asking the user to save credentials is displayed; Confirm it.
8. Refresh the page and click on the "帐号密码登录" link, the left of the 3 links under the QR code to uncover the login form.
9. Notice that the username and password are auto-filled.
10. Clear browser's cache (about:preferences#privacy, Cookies and Site Data, "Clear Data..." button)
11. Refresh the login page and click on the "帐号密码登录" link, the left of the 3 links under the QR code to uncover the login form.

**Expected result**
* Both the email and password are being auto-filled by the Password manager.

**Actual result**
* Only the password is auto-filled, email is not auto-filled.

**Regression range**
* This is not a recent regression.

**Note**
* After saving the credentials by logging into the website, when returning to the login page, only the password is being auto-filled, not the email, also.

**Affected versions**
* Nightly v68.0a1
* Beta v67.0b5
* Release v66.0.2

**Affected platforms**
* Windows 10
* Mac OS 10.13.6
* Ubuntu 16.04

**Steps to reproduce**
1. Open Firefox with a new profile.
2. Reach: https://www.sogou.com/
3. Click on the orange "登录" (login) button from the top-right corner of the screen.
4. Click on the "帐号密码登录" link, the left of the 3 links under the QR code.
5. Input any mail and password inside the input boxes.
6. Click the "Sign In" button.
7. A pop-up asking the user to save credentials is displayed; Confirm it.
8. Refresh the page and click on the "帐号密码登录" link, the left of the 3 links under the QR code to uncover the login form.
9. Notice that the username and password are auto-filled.
10. Clear browser's cache (about:preferences#privacy, Cookies and Site Data, "Clear Data..." button)
11. Refresh the login page and click on the "帐号密码登录" link, the left of the 3 links under the QR code to uncover the login form.

**Expected result**
* Both the email and password are being auto-filled by the Password manager.

**Actual result**
* Only the password is auto-filled, email is not auto-filled.

**Regression range**
* This is not a recent regression.

**Additional details**
* This issue also occurs in the case of qq.com website.
Login page: https://graph.qq.com/oauth2.0/show?which=Login&display=pc&response_type=code&client_id=101487368&redirect_uri=https%3A%2F%2Fpacaio.match.qq.com%2Fqq%2FloginBack%3Fsurl%3Dhttps%3A%2F%2Fwww.qq.com%2F&state=5b481c68e379d