So the problem was also happening on 7 and 8 is that what your saying? And if that is so then did you consider it a Windows issue or site and or bandwidth issue as well? And does other site with file larger then 700mb do the same results or is it just that site? Some times site with large files will detect the download as inactive and terminate the link as well so it also could be site related and that could be the problem as well. So you need to contact whom's google drive your getting the file from and ask if their is some limit download to their files as well.

I never had this issue prior to quantum and if I download the same files on Chrome or IE I do not have this issue occurring thus ruling out the OS or file

As for bandwidth issue if that was the case the file would simply download slowly not freeze firefox and then slow down or freeze windows

I did some additional testing and it seems the issue is occurring with pretty much any large file download

Task manager seems to indicate when downloading ram keeps getting taken up until the download is finished. Once finished ram is freed up and the browser slowly unfreezes

Not sure what else I can do at this point. Im resorting to using chrome for large files

I'm puzzled that downloads from Google Drive would freeze Firefox. I'm pretty sure Firefox would continuously flush the additional bytes out to the Windows TEMP folder, which should put a minimal strain on RAM and CPU. (In contrast to a site like Mega that uses a browser database feature rather than a straight file download.)

Do you browse through any intermediaries, such as filtering software or proxy servers?

I have limited experience with large downloads, just the occasional 600-700MB zip backup file, a content type Firefox has zero interest in handling. After hours I can try some simultaneous downloads to see what happens.

You might also search on the Google Drive forums to see whether this issue has been raised there: https://productforums.google.com/forum/#!forum/drive

I don't use any proxy servers or VPN etc

I updated 2 files to my google drive with 2 different sizes if you want to test.

https://drive.google.com/open?id=1R2igmkWBVsAijMHP3xtL_0zyWKwy2ZeU

About 1GB video file

https://drive.google.com/open?id=1Btip0-mnMjMxC0TGs_68MRkUYJpWMUij

About 3GB video file

I found a fix for me. I had to create a new firefox account. Seems something was syncing across my accounts that may have caused issues

Interesting! I guess you won't know what it was until it starts again (if it starts again).