Looking in Browser Toolbox, it looks like the textfield in question has: ``` appearance: auto; ``` from a UA stylsheet, and that's making it draw the border. I see a similar issue on LastPass as well, installed from https://addons.mozilla.org/en-US/firefox/addon/lastpass-password-manager/ - there's now a black border around the password field on the initial login screen for that add-on, which looks broken because the "Master Password" filler-text gets lifted up to overlap that unexpected-border when the field gains focus.
Bug 1895561 Comment 2 Edit History
Note: The actual edited comment in the bug view page will always show the original commenter’s name and original timestamp.
Looking in Browser Toolbox, it looks like the textfield in question has: ``` appearance: auto; ``` ...from a UA stylsheet, and that's part of what's making it draw the border -- if I set `appearance:none` or `appearance:textfield`, then the border goes away. I see a similar issue on LastPass as well, installed from https://addons.mozilla.org/en-US/firefox/addon/lastpass-password-manager/ - there's now a black border around the password field on the initial login screen for that add-on, which looks broken because the "Master Password" filler-text gets lifted up to overlap that unexpected-border when the field gains focus.