Sometimes a download is halted, perhaps closing a laptop lid, and normal resumedoesn't work. Here is a fix courtesy of orion188:
- You have two files on the destination folder. One with the original name and one with an extra ".PART" extension. Move both of these files to some other folder (Move! not copy)
- Start your download again from the beginning (you have access to the download link, don't you?)
- Let it download a few bytes, just to have those two files created again, with the exact same name. Now PAUSE this download.
- Go to the folder where you backed up those old files. Copy both of these files to your download folder and replace the new created files when asked.
- Now go to Firefox's Downloads form and resume the download.
For me on the second download a .part file was not created, the stream going straight to the destination file. I paused the download, deleted the destination file, and renamed the original .part file to it. From there resume "just worked", colour me happy! :)