/* LIBRARY: detailsPane HIDE tags and keywords */
@-moz-document url-prefix(chrome://browser/content/places/places.xhtml){
 #detailsPane
  :is(.editBMPanel_tagsRow, #editBMPanel_tagsField, #editBMPanel_tagsSelectorExpander, #tags-field-info,
      .editBMPanel_keywordRow, #editBMPanel_keywordField, #keyword-field-info) {
  display:none !important;
 }
}

Add CSS code to the <b>userChrome.css</b> file in the chrome folder in the Firefox profile folder. <hr> <pre><nowiki> /* LIBRARY: detailsPane HIDE tags and keywords */ @-moz-document url-prefix(chrome://browser/content/places/places.xhtml){ #detailsPane :is(.editBMPanel_tagsRow, #editBMPanel_tagsField, #editBMPanel_tagsSelectorExpander, #tags-field-info, .editBMPanel_keywordRow, #editBMPanel_keywordField, #keyword-field-info) { display:none !important; } }</nowiki></pre> <hr> It is not that difficult to create <b>userChrome.css</b> if you have never used it. The first step is to open the "Help -> Troubleshooting Information" page and find the button to access the profile folder with the random name (xxxxxxxx.default-release). *https://support.mozilla.org/en-US/kb/use-troubleshooting-information-page-fix-firefox You can find the button to go to the profile folder under the "Application Basics" section as "Profile Folder -> Open Folder". If you click this button then you open the profile folder in the Windows File Explorer. You need to create a folder with the name <u>chrome</u> in the profile folder with the random name (name is all lowercase). In the <b>chrome</b> folder you need to create a plain text file with the name <b>userChrome.css</b> (name is case sensitive). In this userChrome.css text file you paste the text posted. On Mac you can use the TextEdit utility to create the userChrome.css file as a plain text file. In Windows saving the file is usually the only time things get more complicated because Windows can silently add a .txt or .css file extension and you end up with a file like <i>userChrome.css.txt or userChrome.css.css</i>. To avoid this, you need to make sure to select "All files" in the "Save File" dialog in the text editor. You need to close (Quit/Exit) and restart Firefox when you create or modify the userChrome.css file. More info about userChrome.css/userContent.css in case you are not familiar: *https://www.userchrome.org/what-is-userchrome-css.html *https://www.userchrome.org/how-create-userchrome-css.html *https://www.userchrome.org/firefox-changes-userchrome-css.html In Firefox 69 and later you need to set this pref to true in about:config to enable userChrome.css and userContent.css. *about:config => toolkit.legacyUserProfileCustomizations.stylesheets => true *https://support.mozilla.org/en-US/kb/about-config-editor-firefox