what it does:
after install, your tab bar, address bar and bookmarks bar of firefox will hide automatically when you move the mouse away from the toolbar area after a 350 millisecond delay. they will all reappear when you move the mouse back to the top of the firefox window. the bookmarks bar will also show a maximum of 10 rows at a time so it is more useable. scroll up and down if you reach 10 rows of bookmarks with the mousewheel or the scrollbar on the right. folders within the bookmarks bar expand inline with the bookmarks already there instead of the default behavior. opened folders appear with an outline. when you drag a tab to another window, all toolbars on all firefox windows unhide so you can move the tab without the tab bar hiding. when you download a file, all the toolbars and the download popup display for 4 seconds. since you don't need fullscreen mode when you use this mod, instead of the normal useage, turning fullscreen mode on will make all the toolbars stay open so you can see them all at once along with the whole web page, to give the appearance of temporarily switching off the mod if needed. opening a new tab will no longer automatically put the address bar into focus. this lets the toolbars automatically hide so you can click on something on your new tab page easier. everything works the same maximized and when in a smaller window. this mod works as a replacement for fullscreen mode. you don't have to click fullscreen anymore to hide the toolbars. I also disabled firefox's menu bar, the menu that appears when you press the alt key (with the items file, edit, view, history, bookmarks, profiles, tools and help) since it always appeared accidentally and I never needed it. see the demonstration video here https://www.youtube.com/watch?v=jRXupDJYr14 

pre-requisite:
Firefox or Firefox Developer browser installed in Windows 11. It may work on more versions but I haven't tested them. The latest version of Firefox is recommended but it will probably work on most newer versions. Compatibility issues will arise if your Firefox install is already using autoconfiguration files (such as with Librefox).

installation using installer:
Click here to download https://github.com/botaine/autohide-all-firefox-toolbars-and-expand-bookmarks-bar/releases/download/release/autohide-all-firefox-toolbars-and-expand-bookmarks-bar.zip in releases. extract it, open it then run install.bat . Follow the prompts in the installer. The installer works well when I test it but if it doesn't work for some reason, install manually as described below. running the install.bat file will install the full version, including fx-autoconfig. running the uninstall.bat file will remove everything including fx-autoconfig. some about:config settings will be changed as needed after running the installer (explained in the final confirmation step of the installer) and reverted to default after using the uninstaller. if you already have an existing userChrome.css file in your <firefox_profile>/chrome folder, the installer will overwrite it. <firefox_profile> is not the actual name of the folder, it represents the seemingly random letters and numbers that your firefox profile folder name happens to be. you should rename or move an existing userChrome.css file to save what is already there if anything. you can copy and paste the code from your old userChrome.css file onto the bottom of the new one after running the installer but there is a small chance of a conflict to using both together. open firefox and right click in your tab bar, go to bookmarks toolbar, then click "always show". your bookmarks bar will be shown now on multiple rows and it is probably better this way since it hides when you aren't using it. you can change this setting back to "never show" to hide the bookmarks if you prefer. 

manual installation:
in firefox, open about:config by typing it into the address bar, then seach for toolkit.legacyUserProfileCustomizations.stylesheets . set it to true. this allows firefox to use the userChrome.css file. also in about:config, set browser.fullscreen.autohide to false. This stops firefox's native fullscreen from autohiding the toolbars and allows this mod's fullscreen mode to work as intended. also in about:config, set browser.nova.enabled to false. This stops a gray line from appearing at the top of web pages, caused by a bug in the firefox nova UI. then go to the releases page here https://github.com/botaine/autohide-all-firefox-toolbars-and-expand-bookmarks-bar/releases/tag/release and download autohide-all-firefox-toolbars-and-expand-bookmarks-bar.zip. extract the downloaded zip file by right clicking on it, then click extract all, then extract. this creates a new extracted version of the folder. open it.  put userChrome.css in the chrome folder of your firefox profile. to find that location, in the address bar of firefox type in about:profiles and press enter. then find root directory of the profile in use and click open folder there. the windows explorer location of the firefox profile opens. in that folder create a new folder named chrome if it doesn't exist already, then open it. if it does exist already just open it. put the downloaded userChrome.css file into that chrome folder. if you already have an existing userChrome.css file in your <firefox_profile>/chrome folder(you won't unless you added it), you may not want to overwrite it, so rename or move it. <firefox_profile> is not the actual name of the folder, it represents the seemingly random letters and numbers that your firefox profile folder name happens to be. you should be able to copy the code from the recently downloaded userChrome.css file then paste it to the bottom of the code in your original userChrome.css file, then save it but there is a small chance of a conflict to using both together.

install fx-autoconfig from here so that firefox can use javascripts on the browser UI https://github.com/MrOtherGuy/fx-autoconfig . be sure to complete both the "Setting up config.js from program folder" and the "setting up profile" portion of the install. put all of the downloaded .js files of autohide-all-firefox-toolbars-and-expand-bookmarks-bar into the <firefox_profile>/chrome/JS folder. restart firefox if opened already, or open it if it was closed. right click in your tab bar, go to bookmarks toolbar, then click "always show". your bookmarks bar will be shown now on multiple rows and it is probably better this way since it hides when you aren't using it. you can change this setting back to "never show" to hide the bookmarks if you prefer. the Claude AI can help with install difficulty at any stage. 

configuration:
After installation, here are some settings you might want to change by editing files in notepad. Copy the setting you want to change from below, then open the corresponding file in notepad, use ctrl+f to use the find function, then paste the setting below with ctrl+v to find where to make the change. Make your change, save the file and restart firefox to apply the change. 

The files are located in <firefox_profile>/chrome and <firefox_profile>/chrome/JS . To find your firefox profile location, in the address bar of firefox type in about:profiles and press enter. then find root directory of the profile in use and click open folder there.

In userChrome.css, you can change the number value of --uc-autohide-toolbar-delay 350ms; to any other number in milliseconds to change the toolbar hide delay. I found 350ms is the lowest I could go before the toolbar seems to flicker more than I would like.

In userChrome.css you can change --multirow-bmb-n-rows: 10; to another number to decide how many rows of bookmarks will be shown without having to scroll up and down through them. I used 10 rows because I don't want to scroll often and opening folders on the bookmarks bar takes up more space. 

In download-forceopen.uc.js you can change forceStayOpenFor(4000); to any other number in milliseconds to set how long the toolbars and download pop up will be shown after a download starts or finishes. I find this number lets me see it clearly and doesn't open and close too quickly for short downloads.

Fun fact:
I don't know how to code! I got the Anthropic Claude AI to make it!