Hate the rounded corners inside firefox. Disabled them in windows 11 a long time ago, now you have them inside firefox itself.

[brainetree]

Is the rounded corners inside Firefox something new?  Got rid of them in Windows 11 like a lot of people do and keep them square again after updates and here you betray me.  LOL.

[Agentvirtuel]

Hello

A subject.
https://www.reddit.com/r/FirefoxCSS/comments/1ov0806/does_anyone_know_how_we_can_unround_our_tabs

And, for information purposes.
https://support.mozilla.org/en-US/questions/1546836#answer-1778873

[brainetree]

The dreaded rounded corners are back, what a burden to have to research and find out how to disable it.  Why don't you just give us that option?  I can not accept the rounded corners AT ALL.  Thank you for listening.  I have a lot of other things on my mind, but have to spend no telling how long to figure out how to get rid of those rounded corners.

[Agentvirtuel · Accepted solution]

Hello

Have you tested.

/* In userChrome.css */
:root {
  --border-radius-medium: var(--border-radius-small, 4px) !important;
}

Have you tested.

/* In userContent.css */
@-moz-document url-prefix("about:"), url-prefix("chrome:") { /* Firefox pages like settings etc. */
  :root {
    --border-radius-medium: var(--border-radius-small, 4px) !important;
  }
}

Have you tested, userChrome.css and userContent.css, together.

[kailasanathan_k]

Wait, Does these works in Android?

[upset_ff_oldman]

NOT A SOLUTION. 

[joanofxyz]

this is a horrible answer, I should not have to enable legacy features to disable something when there's a better way to do it

[sam_stoe]

what is this solution? ..a theme or a toogle option should be a solution! 

[Agentvirtuel]

Bonjour

For information
https://support.mozilla.org/en-US/kb/contributors-guide-firefox-advanced-customization
What do users need to know before they use userChrome.css customization?

My answer, replied on 12-02-2026 03:55 AM on Firefox 145.
(e.g.) 7 months ago on Firefox Nightly https://www.youtube.com/watch?v=iEmaI4ciUFM

[brainetree]

Yes Agentvirtuel, I tried those possibilities just as you suggest and they finally worked!  Thank you, what a joy and relief! 

[Agentvirtuel]

Hello

For my part, tested.
https://www.youtube.com/watch?v=iEmaI4ciUFM

[reukiodo]

about:config > toolkit.legacyUserProfileCustomizations.stylesheets > true

about:support > Profile Folder > Open Folder > mkdir "chrome" > edit userChrome.css

/* Force square corners on all Firefox UI elements */
* {
  border-radius: 0px !important;
}

tested on FF 156 and 157

[Agentvirtuel]

Bonsoir

Take Project Nova for a spin in Nightly!
https://connect.mozilla.org/t5/discussions/take-project-nova-for-a-spin-in-nightly/td-p/131273

[reukiodo]

Project nova is the reason I searched for removing the rounded corners. It looks like Apple's silly UI instead of the clean crisp UI Firefox used to have.

[joanofxyz]

absolutely not and I take offense that instead of recommending disabling this program entirely you would suggest enabling legacy styling features that will likely break next time there's an update to this "project"

[upset_ff_oldman]

The solution is NOT the answer and this is fing stupid. You want people NOT to use firefox? This is the way. 

The real fix is to type about:config and type nova and disable all the garbage. 

[Frozen_Baguette]

I love you man, this is exactly what I wanted.

[BushMaster69]

YES! PROBLEM SOLVED!!

[joanofxyz]

this is the real answer

[z0rro37]

Thank you. The CSS solutions only solve the tab buttons, but disabling nova works everywhere.

Disabling browser.nova.enabled was enough. I'll check if disabling the other options is necessary.

[Kstf]

The only good answer.

Thank you for the solution