Windows 10 will reach EOS (end of support) on October 14, 2025. For more information, see this article.

Avatar for Username

Search Support

Avoid support scams. We will never ask you to call or text a phone number or share personal information. Please report suspicious activity using the “Report Abuse” option.

Learn More

This thread was archived. Please ask a new question if you need help.

Black square when a Firefox window is maximized

  • 2 replies
  • 1 has this problem
  • 2 views
  • Last reply by Fantomasas

Fantomasas
Fantomasas
more options

Hello,

Odd rectangular black shadow appears for me when a window of Firefox is maximised (only then). It occurs both in Firefox 57 and 56. Since the first occurring I have reinstalled Firefox at least two times. It hasn’t help.

It started after I reinstalled Windows 10 and installed FF for the first time on a new system two months ago. It happens also for a clear installation of FF, when no extensions are added.

F

Hello, Odd rectangular black shadow appears for me when a window of Firefox is maximised (only then). It occurs both in Firefox 57 and 56. Since the first occurring I have reinstalled Firefox at least two times. It hasn’t help. It started after I reinstalled Windows 10 and installed FF for the first time on a new system two months ago. It happens also for a clear installation of FF, when no extensions are added. F
Attached screenshots

Modified by Fantomasas

Chosen solution

Please Refresh but do this 1st:

then

TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...:

If is your Profile :

Note: Any customization will revert back to default, you will also need to reinstall Extensions.

Please let us know if this solved your issue or if need further assistance.

Read this answer in context 👍 1

All Replies (2)

Shadow110
Shadow110
more options

Chosen Solution

Please Refresh but do this 1st:

then

TEST....... If no issues then Extensions which need to be added back in 1 at a time and tested ..... Or it is your Profile : Make a new one and test ...:

If is your Profile :

Note: Any customization will revert back to default, you will also need to reinstall Extensions.

Please let us know if this solved your issue or if need further assistance.

Fantomasas
Fantomasas Question owner
more options

Thanks for the answer. I have just solved this issue. “Simple Stylish” theme, a very old one, turn out to be a culprit.

https://addons.mozilla.org/en-US/firefox/addon/simple-stylish/

Modified by Fantomasas