Good, even for large files. Rated 4 out of 5 stars
I have 0.9.10. I've had earlier versions as well, and I find them useful for tracking download progress.
If you're downloading a large file (over 2 GB, in my case) then the percent done goes negative, and the status "x MB of y MB" goes negative.
This is a pretty basic mistake (not using large enough integer type, or using units that are too small). BUT, the problem appears to be Firefox's, and not necessarily due to this add-on, as the same thing happens in Firefox's Download window.
Fortunately, this add-on IS able to (eventually) correctly derive an estimated time remaining, which Firefox alone is unable to do at any point.
It would be nice if this could completely compensate for Firefox's defect, but having the time correct does help a bit.