I'm sitting on a 1Gb/s fiber optic connection but cannot upload faster than 1Mb/s to Shutterstock via FTP.

Fotolia at least allows a speed of 21Mb/s

I'm using Filezilla which used to work a lot better than now. For comparison purposes I tried the FireFTP addon for Firefox but there I get only 500kb/s.

I have Kaspersky Internet Security 2017 running and was wondering if anyone achieves faster upload speeds than 1Mb/s to SS and which FTP software/Internet Security they use.

Any tips?

Same here but slow speed only for video!

Yes for footage. Sometimes it peaks at 3Mb/s but then drops down to 1Mb/s again.