Or at least what worked for me anyway.
So I've been stressing about this all day wondering if it was just a server issue or what but more and more people kept posting about upgrading so I couldn't help but think it was something on my end. The client would simply not update for me so I kept trying to update but to no avail. So I uninstalled and I tried accessing Lock's website but it would give me the error message about cookies when I tried to click the download page. The rest of the site worked fine. I kept wondering what the hell the problem was but then I realized something.
The cookies, cache, and history are what were causing the problems. Firefox will store the pages you visit so that it's a faster browsing experience. The problem with this is that Lock updated their download page recently and Firefox has the old download page stored. Firefox isn't searching for the new download page because it's set to search for the same exact one that's in your history. So you have to clear a few things out and you should be able to download the client that will install with no problems, or at least this was my experience.
So the way you fix this is you click the Firefox button > history > show all history (or Ctrl+Shift+H). Now you see the search history bar in the top right hand corner of the window you just opened? Type in "Lock Poker" and delete EVERYTHING that pops up just to be safe. Now you delete your cache and your cookies. Restart Firefox.
Now you can access Lock's website and the download should pop up for you just fine! Hope this helps someone out