A couple others users reported this in the past couple days, but I don't think the cause has been identified.

Are you now using the new version at https://outlook.live.com/owa/?

When I click New, there is a considerable delay, maybe 5 seconds, and then a new window opens. Similarly, when I click Reply, there is a delay. But I do get a window.

Could you add a popup permission "Allow" exception? You can set that using the Permissions panel of the Page Info dialog.

You can call that up using any of these:

• right-click (Ctrl+click) a blank area of the page and choose View Page Info > Permissions
• (menu bar) Tools menu > Page Info > Permissions
• click the padlock or globe icon to the left of the site address, then the ">" icon, then More Information > Permissions

Scroll down to "Open Pop-up Windows" and uncheck the "Use default" box, and then select Allow.

Does that help at all?

Hi kew1, do you have Firefox set to "Accept third-party cookies: Never"? With that setting, Firefox 45.0 was not able to load some sites completely. This is fixed in Firefox 45.0.1, and users have reported that this solves the problems with Outlook.com.

If you haven't already, can you update to Firefox 45.0.1? You can trigger that using the About Firefox dialog as described in this article: Update Firefox to the latest release.

Does the patch fix Outlook.com for you?