Firefox 91: new ESR version will be released tomorrow

Archive
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New versions of its Firefox web browser on Tuesday 10, 2021. The organization does so every 4-weeks on average, but tomorrow's release is special, as it is the base for a new ESR, Extended Support Release, version of the web browser. 

Firefox ESR versions are maintained for a longer period compared to stable releases. One core difference is that they are released with a specific feature set that is not changed during the lifetime. Security updates and bug fixes are released, but features are not added usually until the next ESR version is released. For more info go here https://www.ghacks.net/2021/08/09/firefox-esr-91-new-esr-version-will-be-released-tomorrow/

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Hi Imacri I know you don't like CSS style sheet but sometimes to fix some of the interface problems cause by Firefox updates the only way to fix them is to use CSS here is a 6 line css file for fixing the white density problem  With the use of only 6 lines of code, in userChrome.css in the Chrome folder, I can still 'tighten' the drop down menus in FF 91 ; although it is hard to tell after which update it might stop working.

userChrome.css

Code:

menupopup > menuitem, menupopup > menu {
  padding-block: 1px !important;
}
:root {
  --arrowpanel-menuitem-padding: 1px 1px !important;
}
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[Tip] New Working Method to Restore Classic Theme and UI in Firefox 91 and Later Versions 
https://www.askvg.com/tip-new-working-method-to-restore-classic-theme-and-ui-in-firefox-91-and-later-versions/ -  August 11, 2021 

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I updated to FF91 today and discovered that the tweak I posted in 89.0 Firefox Release June 1, 2021 (i.e., go to about:config and change browser.proton.contextmenus.enabled to FALSE) no longer removes the excessive padding / white space between menu and bookmark items in the Proton UI.  If anyone comes across a new workaround (other than coding a custom CSS style sheet) I'd appreciate hearing about it.
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Dell Inspiron 15 5584 * 64-bit Win 10 Pro v20H2 build 19042.1110 * Firefox v91.0.0 * MS Edge 92.0.902.67 * Microsoft Defender v4.18.2107.4 * Malwarebytes Premium v4.4.4.126-1.0.1413

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https://www.mozilla.org/en-US/firefox/91.0/releasenotes/  Fixed Link

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https://www.mozilla.org/en-US/firefox/91.0/releasenotes/