I see these two prefs about:config about the default browser check.

• browser.shell.checkDefaultBrowser
• browser.shell.skipDefaultBrowserCheck

You can consider to set these prefs to false via mozilla.cfg to see if that works better. See Configuration:

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

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

A local-settings.js file needs to be placed in the "defaults/pref" folder where also the channel-prefs.js file is located to specify using mozilla.cfg.

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

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

Start mozilla.cfg with a comment line (//).

thanks these options are really helpfull. To set as default option is gone now. But i the selenium script that iam running to automate is not working.

driver.get("www.google.com");

It opens browser but website is not getting triggered. looking into that now. I appreciate your help cor-el