Here is how you can disable the default browser check done by Firefox.
After installing Firefox browser, when you launch it, Firefox checks to see if it already was the default browser, if it’s not, asks the user to make it as default: ‘Firefox is not currently set as your default browser. Would you like to make it your default browser?’.
If you don’t want Firefox to perform the default browser check every time when the browser was launched, follow the below steps to deactivate the same.
Disabling default browser check by Firefox browser on Startup
I .When you see default browser prompt from Firefox, then uncheck ‘Always perform this check when starting Firefox’ and click ‘Not now
III. Vsit Settings > General, and under Startup, uncheck ‘.Always check if Firefox is your default browser’.
1. Visit about:config
2. Search for default and change ‘browser.defaultbrowser.notificationbar’ preference value to false.