Add code to the userChrome.css file below the default @namespace line.

• http://kb.mozillazine.org/userChrome.css

@namespace url("http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul"); /* only needed once */

#placesContext_openContainer\:tabs,
#placesContext_openSeparator {
 display: none !important;
}

The customization files userChrome.css (user interface) and userContent.css (websites) are located in the chrome folder in the Firefox profile folder.

• http://kb.mozillazine.org/Editing_configuration

You can use this button to go to the currently used Firefox profile folder:

• Help > Troubleshooting Information > Profile Directory: Show Folder (Linux: Open Directory; Mac: Show in Finder)

Firefox 28 contains security vulnerabilities. It's best to start a new thread (ask a new question) about the other issues you're having with Firefox 29 and resolve them.

• https://www.mozilla.org/security/known-vulnerabilities/firefox.html

1. Install Stylish and restart Firefox when prompted.
   • https://addons.mozilla.org/firefox/addon/stylish/
2. Open the Add-ons Manager (Ctrl+Shift+A).
3. Click User Styles on the left.
4. Click the Write New Style button at the top. Paste the following in the text box, give the style a name, then click the Save button.

@namespace url(http://www.mozilla.org/keymaster/gatekeeper/there.is.only.xul);

#BMB_bookmarksPopup .openintabs-menuitem,
#bookmarksMenuPopup .openintabs-menuitem {
  display: none !important;
}

If you don't want to install an add-on, you can use the userChrome.css file instead, but I don't recommend it.

• http://kb.mozillazine.org/UserChrome.css