The test is failing in Blink and WebKit:
Might be duplicated of bug #140313 (but I'm not 100% sure).
Created attachment 460303 [details]
Safari 15.5 differs from Firefox but matches Chrome
I am able to reproduce this bug in Safari 15.5 on macOS 12.4 using following link:
Link - https://test.csswg.org/shepherd/repository/d6ef85a87b368138c3221dcb78ef3986b2fa54a7/css21/selectors/first-line-floats-002.xht
Please refer to attached screenshot for other browsers. Chrome Canary 105 follows Safari 15.5, while Firefox shows expected result and render the output in "GREEN". Thanks!