What version are you running?
2.5.3
What's the URL of the page this enhancement relates to, if any?

Describe the enhancement and the motivation for it.
When reviewing a set of changes that spans a large number of files it is often not possible to complete this in a single sitting.
It would be very helpful for the reviewer to be able to mark those files they have completed reviewing so that when they come back to the review later they know where they have gotten to.

What operating system are you using? What browser?
Solaris.  Firefox.
Please provide any additional information below.