Firefox download progress

I don’t know where to ask this question.
In the past when Firefox downloaded a file it created a file with the file name that was being downloaded and .part and it saved the downloaded data there and when the download was complete it saved that .part file under the correct name… So it was possible for other programs to know the progress of the download by watching the size of the .part file.
This behaviour has changed. I have downloaded the same file multiple times and each time the .part file is created and sits there with some small quantity of the file being downloaded - 6.5MB in total… until the download is complete. Is there a new way of reading the progress of the download programatically?