This issues is know in problem for firefox. At my work we were told to not use firefox to open or use web-outlook or anything related to Microsoft products as they don't work well with firefox. I would recommend using IE or maybe Edge on outlook related emails instead.

Hey there,

Outlook's website may be optimized for Microsoft products, but a good website is compatible on most browsers, ideally. However, that is not always the reality, sorry about that.

There is a team, Webcombat team, that evangelizes the functionality on sites like this one.

Please take a screenshot of the peices of the site that do not work and Firefox an add the to a new bug on this site: https://webcompat.com/

Thank you for making the internet better!

If you use extensions ("3-bar" menu button or Tools -> Add-ons -> Extensions) that can block (wanted) content (Adblock Plus, NoScript, Disconnect, Ghostery, Privacy Badger, uBlock Origin) always make sure such extensions do not block (wanted) content.

• make sure your extensions and filters are updated to the latest version
• https://support.mozilla.org/en-US/kb/troubleshoot-extensions-themes-to-fix-problems

Firefox shows the shield icon at the left end of the location/address bar in case Content Blocking is blocking content.

• click the shield icon for more detail and possibly disable the protection

You can check the Web Console about what content is blocked

• "3-bar" menu button or Tools -> Web Developer
• https://support.mozilla.org/en-US/kb/tracking-protection
• https://support.mozilla.org/en-US/kb/content-blocking

Clear the Cache and remove the Cookies from websites that cause problems via the "3-bar" Firefox menu button (Options/Preferences).

"Remove the Cookies" from websites that cause problems:

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Manage Data

"Clear the Cache":

• Options/Preferences -> Privacy & Security
  Cookies and Site Data -> Clear Data -> Cached Web Content: Clear