QTextBrowser doesn't show html content correctly. At least not similar than Qt3TextBrowser or Webview. So it's somekind of regression from Qt3.
Used html tags are listed in Qt documentation so those should be supported:
Attached example shows tree widget windows: Qt3TextBrowser, QTextBrowser and QWebView with same content to compare.
Problem is with <blockquote> and empty <a name="123"> </a>. <a name> ignores <blockquote>. Other is <table> in <dl> list.
Test application in Qt4 with qt3support to see all widgets to compare.