Hi. I have quit the same problem since I changed Windows 8.1 to 10.
Third Edge, Firefox & Chrome say that Garmin plugin is no more supported "Firefox ne prend plus en charge ce module externe".
Only IE recognize my Montana 600 but when I click on "Write", I can quickly read "Processing date to write" with the folder (ex: H:/Garmin/GPX/GC5ND3P.GPX) and nothing happen.
I tried to define Firefox as default program as described by StephandD but plugin not supported !!!
I tried also with 2 different USB cable but nothing better.
I tried also with another computer with 7 and all is OK, as it was with W8.1
My GPS is recognize by Bascamp without problem.
I use Norton Internet Security
Someone could help me to find a solution
Thank you