Suddenly have issues with Firefox not being abel to update..help

All has been well for months using CIS. Now suddenly this week, fire fox which is my preferred browser, cannot update automatically or manually. ???

When fire fox attempts to update, it only goes so far in the process and then a window appears on the screen that reads, " The update could not be installed, ( patch apply failed) "
This has happened numerous times this week.
All has been well for months, with both CIS and Malwarebytes both installed. Until just this week when this fire fox update issue began.
Could this be caused by some latest update to a part of CIS?
Or do you think it is a Malewarebytes issue?

I also have Malwarebytes installed and updated.
Scans by both malwarebytes and Comodo find no infections.
Computer is a desk top E machine, in a home, using XP Pro. V 2002 with SP3 Pentium 3
Please tell me how to correct this.
Thanks