I used to have that problem a few years ago. Every time I updated my Firestorm viewer (I'm using Firefox too), I couldn't get a LM through the website anymore. Then somebody (probably in Firestorm support group) suggested the following:
- Download the official LL viewer, if you don't already have it on your PC.
- Open it, so it is able to automatically update to the latest version. It is not necessary to log in!
- Once it is updated, close the LL viewer again and then use Firestorm or update the Firestorm viewer.
Ever since I am doing that I never again had that problem. Even the dreaded EEP update worked fine so far. It doesn't make any sense to me and don't ask for a tech explanation. But it works for me and that is all I need. 😄