Menu customization

First you need to locate your profile folder. There's a subfolder called "chrome". What you need to do is edit the userChrome.css file. Create it if it does not exists.

You can hide any context menu items by adding the lines to userChrome.css:

#id1, #id2 { display:none !important; }

replacing each of the identifiers #id1, #id2, ... with one of the following:

#context-back
#context-blockimage
#context-bookmarklink
#context-bookmarkpage
#context-copy
#context-copyemail
#context-copyimg
#context-copyimg-contents
#context-copylink
#context-cut
#context-delete
#context-forward
#context-metadata
#context-openlink
#context-openlinkintab
#context-paste
#context-reload
#context-saveimage
#context-savelink
#context-savepage
#context-searchselect
#context-selectall
#context-sendimage
#context-sendlink
#context-sendpage
#context-sep-open
#context-sep-stop
#context-setWallpaper
#context-stop
#context-undo
#context-viewbgimage
#context-viewimage
#context-viewinfo
#context-viewpartialsource-mathml
#context-viewpartialsource-selection
#context-viewsource
#openintabs-menuseparator
#openintabs-menuitem

Example (hides the "View Background" menu item and the horizontal line after it):

#context-viewbgimage,
#context-sep-viewbgimage
{display: none !important;}

That's it. Grammar corrections are welcome :)