Canonball said

I ,therefore, removed all files for Firefox and Thunderbird as suggested.

Did you delete the Program Files folders they were installed in?

Yes its the first folder I deleted.

Just to be sure you understand what you need to do:

You need to remove Firefox (and Thunderbird) program folder.

• (32 bit Windows) "C:\Program Files\Mozilla Firefox\"
• (64 bit Windows) "C:\Program Files (x86)\Mozilla Firefox\"

If that still gives problems then reboot the computer and possibly disable security software.

It is possible that security software (anti-virus, firewall) is causing the problem. Try to disable security software temporarily to see if that makes a difference.

Hi everyone....Thanks for the suggestions. I have managed to reinstall Thunderbird but when I have reinstalled Firefox at the end it has the couldn't find XPCOM message. I have removed it using ccleaner, removed Mozilla Maintenance service ensured all folders are removed from Program files 32 and 64 bit and all reference for appdata. downloaded the latest ver 45.0 and reinstalled but still the same message. I still cant get chrome to start not that I need it but I don't like Edge and all my Microsoft Office apps wont load i.e Word Excel etc.. I still think this may be due to Win 10 update last week. Any suggestion would be a help. many Thanks.

Try to install Firefox in Windows Safe Mode after you have deleted the Firefox program folder.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen or hold down the Shift key) to see if that works.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10