Add code to the userChrome.css file below the default @namespace line.

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

:root[inFullscreen] #PersonalToolbar {
  visibility: visible !important;
}

Note that you need to have the Bookmarks Toolbar visible in normal mode.

It is not that difficult to create userChrome.css if you have never used it.

The first step is to open the "Help -> Troubleshooting Information" page and find the button to access the profile folder.

• https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox

You can find this button under the "Application Basics" section as "Profile Folder -> Open Folder". If you click this button then you open the profile folder in the Windows File Explorer. You need to create a folder with the name chrome in this folder (name is all lowercase). In the chrome folder you need to create a text file with the name userChrome.css (name is case sensitive). In this userChrome.css text file you paste the text posted. On Mac you can use the TextEdit utility to create the userChrome.css file as a plain text file.

In Windows saving the file is usually the only time things get more complicated because Windows can silently add a .txt file extension and you end up with a file named userChrome.css.txt. To avoid this you need to make sure to select "All files" in the dialog to save the file in the text editor using "Save File as".

You need to close (Quit/Exit) and restart Firefox when you create or modify the userChrome.css file.

See also:

• https://www.userchrome.org/what-is-userchrome-css.html
• https://www.userchrome.org/how-create-userchrome-css.html

In Firefox 69 and later you need to set this pref to true on the about:config page to enable userChrome.css and userContent.css in the chrome folder.

• toolkit.legacyUserProfileCustomizations.stylesheets = true
• https://www.userchrome.org/firefox-changes-userchrome-css.html

Thank you for your prompt reply, however the results are the same as the default before I created the userChrome.css file. I press F11 to go into full screen then move my mouse to the top of the screen and I get two rows 1) Tabs bar 2) Search and Tool bar. I am looking for a third row which would display my Bookmarks Toolbar. Thank you for your help, but the code is not doing what I need.

Is the Bookmarks Toolbar enabled in a normal window (i.e. a not Full Screen window) because this is a requirement ?

Were you already using userChrome.css or is this your first use of this file?

Did you place the file in the correct location and did you verify that the file doesn't have a hidden .css or .txt file extension ?

Yes the Bookmark Toolbar is enabled in a normale window. This is the first use of the userChrome.css file in this version of FireFox 71.0, however some time ago I have used a userChrome.css file in an older version of firefox. Yes, it is in the correct user profile and I create a Chrome folder and the userChrome.css file with the correct extension.

The folder name of Chrome is incorrect. Firefox won't recognize or use that folder when it has a capital C.

A lower-case c is needed, as in chrome for the folder name.