Downloaded Firefox 4 but message comes up 'cannot open Firefox 4. Not supported on this system.,
I have been using Firefox 3.6.16. successfully for years, occasionally updating.
As suggested, I now downloaded Firefox 4. The Firefox 4 icon is on my desktop and also I have dragged it into my Applications file. On trying to go futher I am told it cannot be opened on this system. I am using MAC OS X, 10.4.11
For older Macs that aren't supported in Firefox 4.0, try TenFourFox for PowerPC's running Mac 10.4.11 & 10.5.8 .