Hello Once again, I open this thread because nobody is warning about this error. This is the third thread, the previous two threads were archived because it was a long time without being resolved and they were closed automatically (each 6 months). So this error is officially active more than one year... Since Firefox v38. Here is the 1st thread (closed automatically after 6 months) https://support.mozilla.org/en-US/questions/1064914 Here is the 2nd thread (closed automatically after 6 months) https://support.mozilla.org/en-US/questions/1099678 And here we are, once again. Firefox v48 with same visual error. Please, before asking and add solutions, read the previous two threads closed, because there are much more information about other solutions that have already said and have not solved anything. Summary: "Since I upgraded to version 38 of Firefox on Mac, I have a problem with the Private Browsing window This is not a functionality issue. It is a visual problem exactly. With a normal window, the top bar you can see normally as always https://i.imgur.com/eghXt2i.png But opening a new private window, you can see that in the top navigation bar, letters are cut at the base https://i.imgur.com/1P12vJR.png Also functional system buttons "Close, Minimize and Full Screen" appear moved up on the bar https://i.imgur.com/U68TUm6.png " Thank you.