Unable to upload

[Cryptogram]

I have been unable to upload things to websites: for example I cannot upload an avatar to these forums (well below the file size limit) and other sites including other forums and file sharing ones. I have tried other browsers (I use Firefox), including the Steam client and I've check that it isn't my firewall. However I can add and send email attachments and uploading university work to sumbit is fine.

 

I strongly suspect the problem lies with my router. When running a internet speed test (speedtest.net) my upload speed it very low at 0.35 Mbps (compared to a downloads speed of 2.18 Mbps with a ping of 45 ms). Does any know what port/protocol such uploading uses? Or do you know what else may be the cause of this problem? Any help would be much appreciated.