Improvements to the website certificate viewer, with more features and more detailed information
Improvements to the extensions downloads API for handling download failures
Extension popup windows now include the extension name instead of its moz-extension:// url when using the windows.create API
Extension-registered devtools panels now interact better with screen readers
Some Windows users who had previously installed and uninstalled Comodo antivirus software may not be able to start Firefox. Information on how to resolve this issue is described on support.mozilla.org or in the support knowledgebase.