I just noticed that I can click on a URL in the Code Editor and it will open in my browser, but I can not click on the same URL in the WYSIWYG Editor and open it.
I know this is to facilitate editing the document, but one solution would be setting up CTRL+Click to open URLs as most word processors do.
Joplin 1.0.233 (prod, linux)
Client ID: 6f4b93ed952d4101b23305e43d9e642b
Sync Version: 1
Profile Version: 32
Keychain Supported: No
Revision: e63eee8 (master)
I am new to Joplin and work on a Windows 10 PC. I had the same problem with a URL in WYSIWIG Editor and did find someone else mention to use CTRL + LEFT CLICK.
It did not seem to work as the mouse cursor never changed to a pointing finger. I then noticed that a Chrome Browser screen I had previously opened under the Joplin Screen had changed. I realized that even though the mouse cursor had not changed the CTRL + LEFT CLICK did open the URL as a PopUnder screen.
I was happy as that will work for me! 
Joplin 2.8.8 (prod, win32)
Sync Version: 3
Profile Version: 41
Keychain Supported: Yes
Revision: c2a6a13