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See this thread about using code in userChrome.css.

• /questions/1265173 Why will toolbars not hide in full screen mode?

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

See:

• https://www.userchrome.org/firefox-changes-userchrome-css.html

Thank You! That did the trick, plus opened the door to a whole bunch of style customization that I can do to Firefox!

This method doesn't work in my Firefox 79.0 (my system is Mac OS 10.15.6) I have set toolkit.legacyUserProfileCustomizations.stylesheets value to true ,created the userChrome.css file in a folder named chrome and put them in profile folder. But the toolbar still not hide in fullscreen mode...

It hide Toolbar Yes ! great work thank you but i see something when i type something in address bar it loads lot of search suggestions based on my history + google but i cant see all the list in the drop down but only a half of first result On my Macbook pro on Catalina OS some how in not-full screen mode its fine. Help please ! Do we need to add some CSS to address bar maybe like z-index ?

It hide Toolbar Yes ! great work thank you but i see something when i type something in address bar it loads lot of search suggestions based on my history + google but i cant see all the list in the drop down but only a half of first result On my Macbook pro on Catalina OS some how in not-full screen mode its fine. Help please ! Do we need to add some CSS to address bar maybe like z-index ?

I have had this issue for as long as I can remember and tonight it bothered me enough to spend over an hour trying to fix it, only to find there is no fix!

Why on earth does Firefox have an issue to "hide toolbars" if it does absolutely nothing on Mac's?

NO this is not an issue with my profile. It's reproducible on a fresh install of macOS and Firefox.

Yes there are add-ins and CSS tricks but they are hit or miss and either don't always work, or come along with other issues.

Why is it so hard for Firefox to fix such a fundamental feature?