That shouldn't happen if you are checking your email online in Firefox, so I assume you're viewing your email using a separate program. Is it one of the usual suspects like Windows Mail, Microsoft Office Outlook, Thunderbird, etc.?

Thank you for your response. I am using MS Office Outlook 2010 Regards

DStewart said

I am using MS Office Outlook 2010

Hey, me too. And now I see what you mean: The "View in Browser" that runs from the header always uses IE, while "View in Browser" in the message itself (if listed) is a standard link, so it uses my default browser, Firefox. (Screenshot attached.)

It seems -- I haven't tried it myself -- that changing this is a two part operation. What Outlook does when you click that button is convert the message to an MHT file, which is an archival format invented by Microsoft, and then launches the file in the default program for .mht files, which is normally IE.

You can:

(1) Install an add-on in Firefox that allows it to display .mht files, and then (2) Make Firefox the default application for opening .mht files

There are two traditional extensions you could consider. According to reviews, they are not compatible with one of Firefox's newer features, which is multiprocess (separating interface and content). If things are not working as expected, you could disable multiprocess (details at the end).

• Mozilla Archive Format, with MHT and Faithful Save
• UnMHT

Source: View in browser opens in IE8 instead of Firefox - Microsoft Community

Multiprocess. Recent versions of Firefox are migrating more users to a "multiprocess" architecture where the user interface and the web content are in separate processes to improve stability. 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 improvement?

Thank you for your help. I tried the solution in " View in browser opens in IE8 instead of Firefox - Microsoft Community" and loaded the unMHT add-on and changed the app to open mht. and mhtml. files in Firefox. Seems to work fine now. Will deal with any problems with incompatibility when they happen. The version of unMHT I installed says it is compatible with Firefox version 53 which is my version.

Regards, Don Stewart.

Hello friend The best solution of your problem is-- go to settings>click find a settings(on upper right corner)>search DEFAULT APP SETTING OPEN IT There are separate setting of email view where you can choose default browser setting for email. just apply according to your wish. See screenshot below