Firefox does not comes with such option for you to change the context menu, so we have to rely on the menu editor extension to get the thing. With this extension, you can now edit your context menu (and any other menus), rearrange the options, hide the unnecessary and even add entry from other menus.
Installation
Install the menu editor addon from here. Alternatively, you can search for it in the Firefox Addon section. Note: If you have problem getting it to work because of incompatible Firefox version, you may want to install the Compatibility Reporter first before install the Menu Editor addon. After the installation, go to the option page for menu editor (you can find at the “Menu Editor -> Preferences” at the Addon section).
Usage
There are two modes: Simple and Advanced.
The simple mode allows you to rearrange the item and/or hide the unnecessary one. First, choose the menu that you want to edit. The default is the context menu.
To rearrange, simply drag and drop the items to the order you want. That’s it To hide it, simply uncheck the tick under the visible field. You will now see a “X”.
In the Advanced mode, you can add items from other menus. For example, to add the “New window” option to the context menu, go to the Advanced mode. On the left pane, make sure the context menu option is selected. On the right pane, select the File menu. Next, drag the “New Window” entry from the right pane to the left.
That’s it. Menu Editor extension for Firefox