[Affected versions]:
Fx 67.0b8
Fx 68.0a1
Fx 66.0
Fx 64.0
Fx 60.5.0esr

[Affected platforms]:
Windows 10 x64
Ubuntu 18.04 x64
macOS 10.13.6

[Steps to reproduce]:

1. Launch Firefox.
2. Saved some logins (username and password).
3. Go to Hamburger menu/Options/Privacy & Security/Logins and Passwords section, click on Saved Logins button.
4. Edit the Username cell then minimize/maximize this window. When you edit the password column after choosing to Show Passwords, then minimize/maximize this window, the issue is present.
5. Go to Hamburger menu/Logins & Passwords menu item, edit the Username or Password cell, minimize/maximize this window, the issue is present.

[Expected result]:
The edited text box remains on position.

[Actual result]:
The edited text box is moving to the right/left.

[Regression range]:

• I will investigate this as soon as possible.

[Notes]:

• On Fx 67.0b8, 66.0 and latest nightly builds, under the edited text box you will see the username again (see: EditUsernameCell67-68.png)
• On Fx 64.0 and 60.5esr builds, the edited text box moves to the right/left but under this selection the username is not duplicated (see: EditUsernameCell64-60.5esr.png)

Probably related to bug 1523957.

I've tried to use mozregression in order to find a regression window, however, the issue is reproducible back to 46.0a1. The older builds are not working properly so I can't go further.

application_buildid: 20160101030330
application_changeset: 22f51211915bf7daff076180847a7140d35aa353
application_name: Firefox
application_version: 46.0a1

Based on comment 2, removed regressionwindow-wanted keyword.

Isn't this a dupe of https://bugzilla.mozilla.org/show_bug.cgi?id=1533739 ?

The comments in bug 1533739 suggest that this was already fixed a few weeks ago with https://hg.mozilla.org/mozilla-central/rev/72c8227148dd in bug 1532863. Gyula Palko confirmed with mozregression here https://bugzilla.mozilla.org/show_bug.cgi?id=1533739#c12.