Hi

I think you are trying to find the new Forget button, which will help you to manage your web history in Firefox.

It may be the case that you need to add it to your toolbar. I recommend you follow this guide that will walk you through how to do this.

I hope this helps, but if not please come back here and we can look into a different solution for you.

You're not running in the Private Browsing mode are you? "Mask" in the titlebar?

You may want to check Options > Privacy -> History and make sure that you don't have Always use Private Browsing mode selected - where there is no visual indication that you're in Private Browsing