Which of the following functions do modern web browsers provide for user convenience?

Modern web browsers are designed to enhance user experience, and one of the conveniences they provide is ad-blocking. Ad-blocking allows users to prevent unwanted advertisements from displaying while they browse the internet. This serves several purposes, such as reducing distractions, speeding up page loading times, and enhancing privacy by blocking tracking scripts embedded within ads.

While file uploading is a feature that browsers support, it is primarily a standard function rather than a specific user convenience unique to modern browsers. Tracking user location is indeed a function supported by modern web technologies but requires user consent and can raise concerns about privacy. Database optimization is not a function provided by web browsers at all; it relates more to server-side operations rather than client-side browser capabilities.

Thus, ad-blocking stands out as a distinct convenience that directly impacts the user's browsing experience, making it the correct answer in this context.