FireFox Web Debugging Tools

I normally work from home as a technical web designer anything PHP,MySQL,Perl,ColdFusion,CSS,JavaScript,XML etc etc and think myself pretty up to date, well for the past few weeks I've been working on a contract with another programmer Hanif and he's showed me the Error Console in FireFox which lists and indicates HTML,CSS and Javascript errors, when I said how useful I found that he then showed me the FireFox add-ons FireBug and web Development which I found sensational.

What I'm trying to say here is how useful it is to co-operate with other experts and also of course how wonderful Firefox is

Solution: Debugging a Difficult Progam Error

Every now and again you come across a really difficult bug where you cannot for the life of you see what's wrong, you've narrowed the bug down to just a few lines of code but still cannot solve it. How to solve it?

Well the reason you cannot debug it is because ONE FACT THAT YOU HOLD TO BE ABSOLUTELY TRUE IS ACTUALLY FALSE.

This means that you assume that a variable contains a certain value , etc or that a function you call cannot contain a bug, it doesn't matter you are turning a BLIND EYE to the problem.

The Solution: Write down your ASSUMPTIONS and then test each one