In the email, they say the web app will not longer be available, that can be a little confusing as it's not the same thing as the web browser version. Some apps have pc version and the browser version which is different.
You mean browser extension?
I am very sure that what it means is the web browser.
If you visit their official site right now and wants to login, you will see this:

The exchange only has mobile apps.
Edit:
Let me simplify it. Web apps still will make use of your browser. Just regard it as you are connecting through your mobile browser through the URL. They are totally different from browser extensions.