How to disable the Nova Design in Firefox
For those not enjoying the new Firefox 157 Nova theme, there is a tweak to restore the tab shapes and old menus.
1-To restore the classic look and disable Nova in Mozilla Firefox, do the following.
2-Open a new tab, and type about:config in the address bar, then hit Enter.
On the Advanced Preferences page that opens, click Accept the Risk and Continue.
3-In the search box, type browser.nova.enabled.
4-In the list below, click on the button with the opposite arrows next to the browser.nova.enabled setting, so it changes its value from true to false.
Source: https://winaero.com/how-to-disable-nova-in-firefox/
Before:
After:
