Open Firefox. Have it declared as the default browser,

Type about:preferences#general<enter> in the address bar. Turn on Always Check Firefox Default Browser.

See also:

• https://support.mozilla.org/en-US/kb/how-make-web-links-open-firefox-default
• https://support.mozilla.org/en-US/kb/setting-firefox-default-browser-does-not-work

FredMcD said

Open Firefox. Have it declared as the default browser, Type about:preferences#general<enter> in the address bar. Turn on Always Check Firefox Default Browser.

Thank you! Will this change apply to all users or will it only apply to my own user account? I have administrator privilege, but most other users are power users.

I think this is a system setting.

There is a command line flag: -setDefaultBrowser

• https://developer.mozilla.org/Command_Line_Options

You can also consider to use the mozilla.cfg file to set or lock some browser.shell prefs that deal with the default browser as found on the about:config page.

You can use the mozilla.cfg file in the Firefox program folder to set or lock preferences and run privileged JavaScript code.

The mozilla.cfg file needs to be in the main Firefox program folder.

These functions can be used in the mozilla.cfg file:

defaultPref();	// set new default value
pref();	// set pref, allow changes in current session
lockPref();	// lock pref, disallow changes

This requires a local-settings.js file in the "defaults/pref" folder where the channel-prefs.js file is located that specifies to use mozilla.cfg.

pref("general.config.filename", "mozilla.cfg");
pref("general.config.obscure_value", 0);

The mozilla.cfg file and possibly local-settings.js need to start with a comment line (//).

See Configuration:

• https://developer.mozilla.org/en-US/Firefox/Enterprise_deployment

See also:

• http://kb.mozillazine.org/Locking_preferences
• http://mike.kaply.com/2012/03/16/customizing-firefox-autoconfig-files/