It didn't include the image for some reason:

https://i.imgur.com/Sus9utT.png

That's probably a left over border from something that is set to have a zero width or otherwise not completely hidden.

I don't see any black borders on Windows, but there is a gray one separating the site identity area from the address area.

If it's someone else's theme, maybe you can alert them to this issue?

Are you using an extension or code in userChrome.css to hide location bar item?

Start Firefox in Safe Mode to check if one of the extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: "3-bar" menu button or Tools -> Add-ons -> Appearance
• Do NOT click the "Refresh Firefox" button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes

jscher2000 said

That's probably a left over border from something that is set to have a zero width or otherwise not completely hidden. I don't see any black borders on Windows, but there is a gray one separating the site identity area from the address area. If it's someone else's theme, maybe you can alert them to this issue?

I found the issue, but it's something hardcoded into firefox:

.urlbar-input-box, #urlbar-display-box { padding-inline-start: 4px; border-inline-start: 1px solid var(--urlbar-separator-color); border-image: linear-gradient(transparent 15%, var(--urlbar-separator-color) 15%, var(--urlbar-separator-color) 85%, transparent 85%); border-image-slice: 1; }

If it inspect element on chrome://browser/content/browser.xul I can find the CSS rule above. removing the border-inline-start fixes the problem. How can I use this?

See:

• https://developer.mozilla.org/en-US/docs/Web/CSS/border-inline-start

chrome://browser/skin/browser.css

cor-el said

See:

• https://developer.mozilla.org/en-US/docs/Web/CSS/border-inline-start

This does not help...

I don't need an explanation on what it is. I know what it is.

I'm trying to remove it from the address bar

Where are you in the process of overriding that rule? Have you tried putting something like this in userChrome.css or a Stylish user style?

.urlbar-input-box, #urlbar-display-box {
  border-inline-start: 1px solid transparent !important;
  border-image: none !important;
}