If you want to remove the browser control buttons from the context menu in Firefox, it's a very easy tweak that doesn't require any add-ons. You just need to add a few lines to the userChrome.css file for your Firefox profile.

Where is userChrome.css?

This file does not exist by default, so you'll have to create it if it hasn't been created already. Navigate to the Firefox Profiles directory:

Windows Vista & 7:
C:\Users\USER\AppData\Roaming\Mozilla\Firefox\Profiles
Windows XP:
C:\Documents and Settings\USER\Application Data\Mozilla\Firefox\Profiles
In this folder there will be one or more Firefox profile folders. A Firefox profile folder has a random string of alphanumeric characters as its name. The one with "default" in its name should be your primary one. Open it and create a folder called chrome inside. Then create a file called userChrome.css inside the new chrome folder.

Be sure to turn on Windows file extensions to make creating files with specific extensions easier.

Here is an example of the location of userChrome.css on my Windows 7 PC:
C:\Users\Nick\AppData\Roaming\Mozilla\Firefox\Profiles\asdf12345.default\chrome\userChrome.css

CSS Tweak

Open userChrome.css in a text editor such as Notepad and add this content:

#context-back image,
#context-forward image,
#context-reload image,
#context-stop image,
#context-bookmarkpage image,
#context-navigation,
#context-sep-navigation {
display:none !important;
}
Now restart Firefox and the context menu controls (back, forward, etc) should be gone.