I purchased my FIMK via dgex.com and I've now downloaded the browser web wallet; so next step presumably is to go to
https://wallet.fimk.fi:7886/, click on
Returning User?, enter the passphrase for my FIMK account, as set out in my dgex.com back office, wait for the blockchain to download and start forging.
Is that it or have I missed a step?
Thought I should check first.
TIA

You should download and run the wallet on your own machine. You seem to say you did that. I would trust the web wallet is forging for me.
If you downloaded the wallet and ran that run.bat you should browse to localhost:7886 and login. You should see your wallet. From there you can "logout" and keep the wallet running on your PC and you will be forging.