How to remove `t=canonical` from Firefox browser searches made on DuckDuckGo?

In Ubuntu 14.04, when I do a search in Firefox using either the address bar or the search bar, the system always adds t=canonical to my searches. So the full string becomes: https://duckduckgo.com/?q=cat+cooking+salmon&t=canonical.

However, if I perform the same search by going directly to the search engine, i.e. typing the search engine name and doing the search from the presented search box, this does not happen. In this case the string is: https://duckduckgo.com/?q=cat+cooking+salmon.

How do I stop Ubuntu/Firefox from adding t=canonical to my search queries? And, why is this behavior there in the first place?

&t=

Through partnerships with developers and companies, DuckDuckGo has been integrated into many applications. In these partnerships, a portion of DuckDuckGo's advertising revenue is sometimes shared back. To assign advertising revenue and collect anonymous aggregate usage information, developers add a unique "&t=" parameter to searches made through their applications.

If you want to remove it, edit the file:

/usr/lib/firefox/distribution/searchplugins/locale/*language-here*

Edit all the languages just to be sure.

Edit for 20.04

1. Open Firefox, navigate to Preferences --> Search, and remove the per-installed DuckDuckGo search engine
2. Download the search engine new from the Firefox Add-ons directory. Select this as the default search engine in the preferences The string, &t=canonícal, ceased to insert itself into the searches via the address bar thereafter. With help from Komalleana Byzantis

Below are before and after pictures:

^{Source:DuckDuckGo Forums}

Read the output from apt-cache show xul-ext-ubufox. Here's a partial quote:

Package: xul-ext-ubufox
Priority: optional
Section: web
Installed-Size: 378
Maintainer: Ubuntu Mozilla Team <[email protected]>
Architecture: all
Source: ubufox
Version: 2.8-0ubuntu1
Replaces: ubufox (<< 0.9~rc2-0ubuntu3)
Provides: firefox-ubufox, ubufox
Depends: aptdaemon, libglib2.0-0 (>= 2.26)
Recommends: firefox (>= 9.0)
...
Description-en: Ubuntu-specific configuration defaults and apt support for Firefox
 Adds Ubuntu-specific modifications to Firefox.
 .
 Integrates the browser with Ubuntu to:
  * Enable searching for missing plugins from Ubuntu software catalog
  * Add the following options to the Help menu
    - Get help on-line
    - Help translating Firefox
    - Ubuntu Release Notes
  * Set homepage to Ubuntu Start Page
  * Display a restart notification after upgrading Firefox
  * Add ask.com to the search engines.
 .
You can uninstall this if you prefer to use a pristine Firefox install.
Enhances: firefox
Homepage: https://launchpad.net/ubufox

Note the third-last line.

As for why, Canonical may earn some revenue but that's just speculation.