Maybe one of the following?

If the Problem is with Outlook Web App on Exchange Server 2010 or Earlier

Firefox removed the showModalDialog script method in Firefox 48, which is similar to a change in Google Chrome 37 a couple years ago. Microsoft has not updated older versions of Exchange to use other script methods, despite the passage of quite a lot of time, presumably because they prefer companies to update.

I'm not aware of a workaround for this problem other than using an old version of Firefox (e.g., 45.9.0esr from April 2017), which raises security concerns.

Possible Incompatibility with Multiprocess

Starting in Firefox 48, but accelerating in more recent versions, Firefox is migrating users to a "multiprocess" architecture where the user interface and the web content are in separate processes to improve stability. Firefox assesses whether your current configuration is compatible during the first run -- first run after installation or first run after a Refresh -- and if it is, enables it going forward for future runs. Could you investigate:

Are you using Multiprocess (e10s)?

Multiprocess creates a second firefox.exe or plugin-container.exe process to isolate the web content from the browser UI. You can check whether you have this feature turned on as follows. Either:

• "3-bar" menu button > "?" button > Troubleshooting Information
• (menu bar) Help > Troubleshooting Information
• type or paste about:support in the address bar and press Enter/Return

In the first table on the page, check the row for "Multiprocess Windows" and see whether the number on the left side of the fraction is greater than zero. If so, you are using e10s.

If you are using e10s:

To help evaluate whether that feature is causing problems, you could turn it off as follows:

(1) In a new tab, type or paste about:config in the address bar and press Enter/Return. Click the button promising to be careful.

(2) In the search box above the list, type or paste autos and pause while the list is filtered

(3) Double-click the browser.tabs.remote.autostart.2 preference to switch the value from true to false

Note: the exact name of the preference may vary, but it will start with browser.tabs.remote.autostart

At your next Firefox startup, it should run in the traditional way. Any difference?

Yes once I set browser.tabs.remote.autostart.2 to false it worked fine. SO can I leave this set to false so my Outlook web app will work correctly or by leaving it set to false will cause an issue?

When multiprocess is enabled, Firefox should be more stable and have better security "sandboxing" but it's certainly not necessary.

I did not do anything with the multiprocessor. It is still on. I only set the browser.tabs.remote.autostart.2 to false and my Outlook works fine. My question still is can I leave the browser.tabs.remote.autostart.2 to false or will that cause an issue?

What should happen when you change that setting to false is that Firefox's built-in multiprocessing feature is disabled in your next session. You should see the difference on the Troubleshooting Information page. That is the context for my comments about multiprocess.

I understand. The issue I have is that I have users that like to use Mozilla with Outlook web app. That is why I asked if it would cause the issue. Is the any other work around or will Mozilla correct this issue?

tony2063 said

Is the any other work around or will Mozilla correct this issue?

I do not have any other information about this issue right now.

Most past threads either had no responses/suggestions, or one of the two I posted, and the person with the question did not even follow up. So you're really the first person who seems to be fully engaged -- thank you!

There is an issue open for this in the bug tracking system, but no progress so far as there was very little information about where the problem might lie. I added information from and a link to this thread for reference.

"After Firefox 51 is not possible to open dialog for attachments, images, addresses, in OWA (web mail)"

• https://bugzilla.mozilla.org/show_bug.cgi?id=1345854
• Bugzilla Etiquette
• Voting

Do you know what version of Exchange Server has this problem, or is your mailbox on Microsoft's hosted Office 365 infrastructure? Note that your company may have a policy against disclosing this kind of information.

Exchange 2010

I remember it well. ;-)

Considering Microsoft's product lifecycle policy, I suspect we won't get any help from Redmond on the server side. https://support.microsoft.com/en-us/lifecycle/search/13965

It's possible someone monitoring the bug will ask you to capture some log information related to the problem to see whether Firefox can work around it. That might reveal it is a more general issue; there are other sites that require this workaround. However, I don't know what priority the work will receive. That can vary enormously...