If a method is used several times at the top of the page, and you want to find out if it's used elsewhere, without the highlights, you don't know that. You have to hit Next until you make sure it's nowhere else. With the highlights, you immediately see that the block you're looking at is it, and you can move on to a different file.

Browsing a large code repository. The scrollbar highlights allow me to "eyeball" the page and go to the general locations quickly rather than hitting Next a thousand times (which feels primitive as hell anyway), especially when a block of code has the same keyword used many times and I need to move on to the next block.

I tried Firefox for a while but I rely on that feature around once or twice a day and I preferred using Chrome for those browsing sessions. So I dumped Firefox and switched back.