User Agent: Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:85.0) Gecko/20100101 Firefox/85.0
Steps to reproduce:
Firefox 83.0 on Windows 10 20H2. I installed an update manually using the full installer from the website 1 and then noticed something was wrong with the new tab search box, it didn't look right.
I was unable to search anything in the new tab search box. After that I opened another new tab and that tab (and every subsequent one) had the proper G icon (for Google search) on the left and I was able to search. I have not been able to reproduce this issue since then.
An animated GIF illustrating the issue is attached.