The original solution was for Firefox 75. Due to changes in Firefox 77, the original solution is obsolete and there are new options.

Firefox supports an optional style sheet file named userChrome.css that we can use to modify the toolbar area, including taming the expanding address bar. Setting up your first userChrome.css file is about a 10 minute project, so when you have time to dive in, here are some threads to check out:

  [[Type in the address bar about:config and press Enter. (ignore the warning)  Type in the search bar and look for the preference :  browser.urlbar.openViewOnFocus  and set its value to false  Do the same with these preferences :  browser.urlbar.update1 (already mentioned by jscher2000)  browser.urlbar.update1.interventions  browser.urlbar.update1.searchTips  Then close and restart Firefox.]] 

   https://support.mozilla.org/en-US/questions/1283911#answer-1303777
   https://support.mozilla.org/en-US/questions/1284030#answer-1304125
   https://www.userchrome.org/megabar-styling-firefox-address-bar.html#mbarstyler 

More background on userChrome.css files: https://www.userchrome.org/

In Nightly, there is a specific preference for this in about:config called browser.urlbar.update1 (previously known as browser.urlbar.megabar).

Setting that to false will revert the bar to its more typical behavior in new windows (the windows that are already open seem to keep the megabar behavior until the next session).

For anyone unfamiliar:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk.

3rd solution:-

The original solution was for Firefox 75. Due to changes in Firefox 77, the original solution is obsolete and there are new options.

Firefox supports an optional style sheet file named userChrome.css that we can use to modify the toolbar area, including taming the expanding address bar. Setting up your first userChrome.css file is about a 10 minute project, so when you have time to dive in, here are some threads to check out:

 [[Type in the address bar about:config and press Enter. (ignore the warning)  Type in the search bar and look for the preference :  browser.urlbar.openViewOnFocus  and set its value to false  Do the same with these preferences :  browser.urlbar.update1 (already mentioned by jscher2000)  browser.urlbar.update1.interventions  browser.urlbar.update1.searchTips  Then close and restart Firefox.]] 

  https://support.mozilla.org/en-US/questions/1283911#answer-1303777
  https://support.mozilla.org/en-US/questions/1284030#answer-1304125
  https://www.userchrome.org/megabar-styling-firefox-address-bar.html#mbarstyler 

More background on userChrome.css files: https://www.userchrome.org/

(2) In the search box above the list, type or paste URLB and pause while the list is filtered

(3) Double-click the browser.urlbar.update1 preference to switch the value from true to false

Note: This preference does not exist in Firefox 71-72.

Note(1):- In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button accepting the risk. Note: This preference does not exist in Firefox 71-72. This preference to turn off the "Megabar" works in Firefox 75 and probably will work in Firefox 76.

Yes this works but I see some problem with bar .I use 2 bars but one is a little low .Which parameter is responsible for put it up.Small bar windows is 1milimiter too low.The should be on the same line .---------------- .Screenshot show problem red arrow.

1. urlbar[breakout],
2. urlbar[breakout][breakout-extend] {

 --urlbar-height: 28px !important;
 --urlbar-toolbar-height: 30px !important;

 width: 100% !important;
 top: calc((var(--urlbar-toolbar-height) - var(--urlbar-height)) / 2) !important;
 left: 0 !important;

}

1. urlbar[breakout][breakout-extend] > #urlbar-input-container,
2. urlbar-input-container {

 height: var(--urlbar-height) !important;
 width: 100% !important;
 padding-block: unset !important;
 padding-inline: unset !important;
 transition: none !important;

}

1. urlbar[breakout][breakout-extend] > #urlbar-background {

 box-shadow: 0 1px 4px rgba(0,0,0,.05) !important;
 animation: none !important;

}

Yes this works but I see some problem with bar .I use 2 bars but one is a little low .

#urlbar[breakout],
#urlbar[breakout][breakout-extend] {
  --urlbar-height: 28px !important;
  --urlbar-toolbar-height: 30px !important;

  width: 100% !important;
  top: calc((var(--urlbar-toolbar-height) - var(--urlbar-height)) / 2) !important;
  left: 0 !important;
}

Hi, I think you need to adjust the value for top: to something higher. Since you use the "normal" density layout, I think, you could try:

top: 5px !important;

and see whether that works for you.

I also have a rules file here if you want to compare: https://www.userchrome.org/samples/userChrome-ZeroEnlargement.css

Yes your file works for me .Thanks you .I do not understand why Team Firefox make our live that difficult.I see how a lot of people in Poland will be like change this for old behavior . Thanks your brother both .

This movie show my me mistake with create userChrome.My mistake was because file has to be in folder """chrome""" then Firefox see this file .

https://vimeo.com/241645477

I'm on FF 77.0.1 and none of the above works for me.

Hi joe80, let's continue with your new question here: https://support.mozilla.org/questions/1290682