Some Software downloaded from the internet come bundle with crapware (crap shitty software) that does nothing but inject your Browser or any software from your computer with ad-ware. A malicious code to serve you ads that you don't want to.
This injection escalate to make your browser open an Unknown Url and there is no setting to remove it. The only way to remove it is via the browser configuration file. Not the setting from the toolbar.
search conduit is one of the famous URL injected to your browser.
For Firefox, type about:config in the address bar. If you encounter any error, simple accept and proceed.
next, in the search box, type, browser.newtab.url. This will narrow down the config list. Double-click the browser.newtab.url below, a dialog box will pop up, and delete everything inside it then click OK. You can also set this to your preferred or favorite website.
Your browser will go back to normal every time you open a new tab.