Please explain the problem in detail. What happens? What is/are the exact error message(s) ?

To log in to M&S Internet Banking you enter a user name and then it asks for a security code. This you get from the M&S app on your phone. You key it in and you are logged in. Or at least you were. Now (as of the last couple of weeks) you key in the security code and nothing happens. No message, just no action.

So as I said I called M&S support and they suggested trying a different browser. I called up Microsoft Edge and followed exactly the same procedure with the difference that this time when I entered the security code I was logged in as usual.

From this I have to assume that something has been changed in Firefox creating some sort of incompatibility with M&S's banking application.

Thanks for your interest, if you can help I will be most grateful.

When you compare in the two browsers, is anything missing from the login form in Firefox, such as a CAPTCHA test or checkbox, etc?

If a site is generally known to work in Firefox, these are standard suggestions to try when it stops working normally:

Double-check content blockers: Firefox's Tracking Protection feature, and extensions that counter ads and tracking, may break websites that embed third party content (meaning, from a secondary server).

(A) The shield icon toward the left end of the address bar usually turns a bit purplish when content is blocked. Click the icon to learn more or make an exception. See: Enhanced Tracking Protection in Firefox for desktop.

(B) Extensions such as Adblock Plus, Blur, Disconnect, DuckDuckGo Privacy Essentials, Ghostery, NoScript, Privacy Badger, uBlock Origin or uMatrix usually provide a toolbar button to manage blocked content in a page. There may or may not be a number on the icon indicating the number of blocked items; you sometimes need to click the button to see what's going on and test whether you need to make an exception for this site.

Cache and Cookies: When you have a problem with one particular site, a good "first thing to try" is clearing your Firefox cache and deleting your saved cookies for the site.

(1) Clear Firefox's Cache

See: How to clear the Firefox cache

If you have a large hard drive, this might take a few minutes.

(2) Remove the site's cookies (save any pending work first). While viewing a page on the site, click the lock icon at the left end of the address bar. After a moment, a "Clear Cookies and Site Data" button should appear at the bottom. Go ahead and click that.

In the dialog that opens, you will see one or more matches to the current address so you can remove the site's cookies individually without affecting other sites.

Then try reloading the page. Does that help?

Testing in Firefox's Safe Mode: In its Safe Mode, Firefox temporarily deactivates extensions, hardware acceleration, and some other advanced features to help you assess whether these are causing the problem.

If Firefox is running: You can restart Firefox in Safe Mode using either:

• "3-bar" menu button > "?" Help > Restart with Add-ons Disabled
• (menu bar) Help menu > Restart with Add-ons Disabled

and OK the restart. A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

If Firefox is not running: Hold down the Shift key when starting Firefox. (On Mac, hold down the option/alt key instead of the Shift key.) A small dialog should appear. Click "Start in Safe Mode" (not Refresh).

Any improvement?

Thank you for your detailed and helpful reply to my query.

I can only assume that M&S have done something to their internet banking application because it has started to work normally again - ie I can log in from Firefox as usual.

regards Andrew Marjoribanks