This week I couldn’t upload big files on Google Drive with Firefox. With Chrome all went well.
Even after deleting the cache and disabling all extensions, it didn’t work.
Though I didn’t think Kasperky would be the cause, I disabled Kaspersky and the upload succeeded!
I found out that I had to disable Network -> Scan secured traffic Firefox and Thunderbird.
So, my problem has been solved, but I mention it in case other members encounter the same problem.