If you do not like the new Nova design in Firefox 157, it is [easy to disable it](https://winaero.com/how-to-disable-nova-in-firefox/). 

Go to **about:config**, and set **browser.nova.enabled** to **false**.
The changes apply instantly.

Additionally, you can set **sidebar.revamp** to **false** to bring back the classic sidebar without extra toolbar/icons on the left.

I [wrote a guide](https://winaero.com/how-to-disable-nova-in-firefox/) with screenshots and details if you need it.