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Hmm, I don't think there should be left and right borders on a maximized window, however, Windows 10 has some differences from Windows 7.

One Windows 10 user who had set the Taskbar to the left side discovered that the borders went away if they moved the Windows Task Bar to the bottom and back to the left side.

You can find the screenshot here where you can clearly see the white borders: https://imgur.com/a/y07vMeY

Was that default FF install or did you use css customizations?

Default install, very little customized and no external profile syncs. I also have a bare minimum of addons installed and it's the default dark theme.

Aelyss said

Default install, very little customized and no external profile syncs. I also have a bare minimum of addons installed and it's the default dark theme.

Remove the theme and return to default and see if anything changes.

Hi, you can check things this way : SAFE MODE

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

In Firefox Safe mode these changes are effective:

• all extensions are disabled (about:addons)
• default theme is used (no persona)
• userChrome.css and userContent.css are ignored (chrome folder)
• default toolbar layout is used (file: localstore-safe.rdf)
• Javascript JIT compilers are disabled (prefs: javascript.options.*jit)
• hardware acceleration is disabled (Options > Advanced > General)
• plugins are not affected
• preferences are not affected

TEST''''is issue still there ?

See Pkshadow's post in this thread :

https://support.mozilla.org/en-US/questions/1197359

which was marked 'Chosen Solution' ......

I've tried in safe mode and the issue persists. I can't uninstall the dark theme from the UI, I can only disable it and that doesn't solve the problem. The "Default" theme has the exact same issue of the border.

I did a little playing around with the windows settings and here's what I've found:

• My primary monitor doesn't have it (external screen 1920x1080)
• My laptop screen has this issue (1920x1080)
• The issue goes away when I change my scale from 125% to 100%

So it seems related to the windows scaling, but as firefox is the only application with this issue, it's probably related to the part where it hides the title bar and integrates the tabs instead. When I have the title bar, the issue isn't present at 125%.

And as I mentioned, I won't uninstall, that's far too much effort for such a simple bug. reinstalling an application should _never_ be a solution to a bug like this! Do not ask people to go through all this effort instead of solving the actual issue!