New search bar with some changes and fixes. 75.0+ version

'userChrome.css'
or 'userChrome_searchbar_noBlur.css' for no blur search bar.

NEW. Added One Line config 'userChrome-ONE-LINER.css'

If you dont like the changes to URL/SEARCH bar it can be reverted with these about:config tweaks. (this will be disabled soon)

browser.urlbar.update1; set to False
browser.urlbar.openViewOnFocus; set to False (your preference, this disables opening on focus, need to type to open search)

and use 'userChrome_old_searchbar.css' for browsers older than 75.0 version. dont forget to rename to 'userChrome.css'

Tested on:

 Windows 10 / 73.0.1 / 74.0 / 74.0.1 / 75.0.0 / 77.0.1 Default Dark Theme
 Linux 74.0.1 / Default Dark Theme

Dont forget to enable 'toolkit.legacyUserProfileCustomizations.stylesheets' in about:config for your custom themes to work.

You can find more in 'userChrome.css'

/* Comment this to show min/max/close buttons. I use OS style firefox plugin. */
  #TabsToolbar > .titlebar-buttonbox-container {visibility: collapse !important;}

/* Width of the tabs. Change it to 100% to get full 
width style tabs. But it looks funny, make search 
bar transparent so it looks better with full width */
	.tabbrowser-tab[fadein]:not([pinned]) {max-width: 135px !important;}  

Blur style search and bookmarks bar. Used the search method found here

Need about:config 'layout.css.backdrop-filter.enabled' = true and it could require the 'gfx.webrender.enabled' to true. But if it works with the 'backdrop-filter' leave this one.

https://www.reddit.com/r/FirefoxCSS/comments/ddi4dc/testing_the_backdropfilter_in_the_url_dropdown/

I use Flexible space for spacing https://imgur.com/a/Gd82v0H

Linux (blur works too after enabling both options mentioned above).