A Firefox colour problem???

I am developing an app using php5 and MySQL to serve data into tables.

I have set two light bgnd colours for alternating table rows... with fine
black text.

Works perfectly when previewed in IE5 (pale green: #B8F8B6 & pale yellow:
#F0F385)

I have just installed Firefox for the first time and was quite horrified to
see both colours to be two shades of very dark blue??? So now you obviously
can't see the black text!

Why is this???   Thanx in advance

Confused 010000111110101001010
01000110011100110011010110010