The coding errors had to do with extra line breaks that interrupted CSS code that specified fonts to be used. The resulting code was not in accord with the CSS2 specification.
I owe FireFox an apology for this and a special word of thanks to Blake Ross.
However, after installing the "improvement" I discovered that this version has less functionality than the earlier version. It cannot even properly select fonts, and Mozilla doesn't intend to fix this problem until 2007.
I tried re-installing 1.0.7, and it will no longer run. I have tried uninstalling everything from mozilla and deleting the directory before re-installing, and it still won't run.
FireFox 1.5 is a disaster.