Download popup panel progress bar overflows

When you click the download button on the toolbar, the progress bar of the downloading items overflows horizontally, making it impossible to view the true progress ratio, and the stop/cancel/continue button on the right side of the items cannot be clicked.

Note that there is no such issue after opening the "Show all downloads" window, the issue only exists in the pop-up window.

This issue has existed for a long time and exists in both TB13/14.

This issue does not exist in the original Firefox.