Is that web outlook? If so then the the outlook settings isn't working correctly. And your going to have to ask Outlook support to fix the issue on their site.

Hey! That sounds like a browser issue try clearing your cache or using a different browser (Chrome or Edge usually work best with Outlook). Also, disable any browser extensions temporarily, some of them mess with Outlook. If that doesn’t help, try Incognito mode to test. Let me know how it goes!

What OS? If windows, home or pro and are you running any security software besides MS Defender? What version of Firefox? Did you try with Firefox in Troubleshoot Mode? https://support.mozilla.org/en-US/kb/diagnose-firefox-issues-using-troubleshoot-mode#w_how-to-start-firefox-in-4troubleshoot-modesf5safe-modesf I have no issues with reply or drafts. see screenshot