Some Mac apps require a round-trip through Safari to authorize activities using a web-based login. For instance, a recent update to Quicken for macOS supports a more secure login method offered by Citi for banking and credit cards. Quicken prompts you to approve the new connection and then opens a window in your browser.
For whatever reason in my case, Safari refused to oblige: it opened the window and let me log in, but it didn’t allow whatever activity Citi wanted to perform. Only a partially loaded page appeared.
After trying some troubleshooting, I realized the easiest course of action was to switch browsers. Quicken lacks an option–like many apps–to choose a preferred browser. Instead, it relies on the default setting in macOS.
Read more at Macworld.com