Have a look here: https://support.mozilla.org/en-US/questions/1294449

^: that thread is from 2020 (Firefox 78) and doesn't apply anymore.

You can hide those context menu items with code in userChrome.css. See this file for the IDs of those items, you need to prefix an ID with a hash (#).

• https://searchfox.org/mozilla-release/source/browser/base/content/browser-context.inc#103

Add CSS code to the userChrome.css file in the chrome folder in the Firefox profile folder.

#context-sep-open,
#context-bookmarklink,
#context-savelinktopocket,
#context-copyemail,
#context-copyphone,
#context-copylink,
#main-context-menu-strip-on-share-link {
  display:none!important;
}

It is not that difficult to create userChrome.css 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 chrome in the profile folder with the random name (name is all lowercase). In the chrome folder you need to create a plain text file with the name userChrome.css (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 userChrome.css.txt or userChrome.css.css. 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

You need to set this pref to true in about:config to enable userChrome.css and userContent.css in Firefox 69+.

• about:config => toolkit.legacyUserProfileCustomizations.stylesheets => true
• https://support.mozilla.org/en-US/kb/about-config-editor-firefox

Strange. I'm on 129 and have spent the time since my earlier post implementing it with success. The Simple Menu Wizard to which it refers was last up-dated three weeks ago for 128.

The CSS I've produced is like yours but longer as I got rid of more junk.

OK, I see that this GitHub files have been kept up to date, but it requires to check a lot of CSS files to find what you items want to remove and you need to remember what you have changed and keep this synced with future updates. I might be easier to keep this as tight as possible to keep overview.