When upgrading to MAMP PRO 5.3 your SSL certificates may not have been copied over, causing your ssl hosts to appear in red.
Please do the following.
1. When upgrading, a copy of your /Applications/MAMP folder was made. This folder is named /Applications/MAMP_XXXXX
2. You need to copy your ssl certificates from /Applications/MAMP_XXXX/Library/OpenSSL/certs to /Applications/MAMP/Library/OpenSSL .