Mozilla/5.0 (Windows NT 6.1; Win64; x64; rv:64.0) Gecko/20100101 Firefox/64.0 Build ID: 20181008100121 Steps to reproduce: - download a file, preferably a big one taking some time - observe the Downloads Panel or the Downloads View Actual results: The progress bar is stuck at 100%, not reflecting the current progress. The "bar" part is green and animated, looking like a native Windows 7 gauge. Expected results: The progress bar should follow the actual progress. The "bar" part should be blue. This is a regression. Could be linked to XBL removal bug 1452626 ?

Is this a regression? Could you try using mozregression to pinpoint what caused the regression?

Yes, it is a regression introduce with Nightly 2018-10-04. Mozregression report: Narrowed inbound regression window from [f7fd7d2c, 5543e7f5] (3 builds) to [0438e11c, 5543e7f5] (2 builds) (~1 steps left) Starting merge handling... Using url: https://hg.mozilla.org/integration/mozilla-inbound/json-pushes?changeset=5543e7f5ddadba11a98f54fef214089ea1f8f3a0&full=1 Found commit message: Bug 1491197 - replace progressmeter XBL binding by a custom element, r=paolo Did not find a branch, checking all integration branches The bisection is done. So that regression was introduced by Bug 1491197, that makes sense.