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

[Simon_M]

I don't firefoxing understand what the firefox does a user have in their mind to accept as "solution" having to mess with custom user firefoxing stylesheets!

Of course ideally it's Firefox Engineering Managers and Product Owners  responsibility to not have foreseen that an option to toggle this firefoxing rounded corners off would be mandatory, but at least they should have pushed this as an experiment to a subset of trusted testsers before delivering it to the mainstream.

But your suggestion to use `about:config` setting to toggle it is clearly the right solution.

[Jibun-no-Kage]

HATE, HATE, HATE the new FireFox theme, look, HATE, HATE, HATE, IT. And you don't even give users a way to disable it with ease... IDIOTS.

And browser.nova.enabled is not working for some reason on my firefox.  (Windows 11 PC).