I don't want to burst anybody's bubble here, but great as firefox is from the end user experience, it's horribly resource hungry and crawls on machines with far more horsepower than any genuine 68K amiga has available.
The same is true of open office and a lot of other things on the list. When the Open Source guys start projects like this, they are typically aiming at mainstream systems, not decades old machines that have a tiny fraction of the horsepower available.
There's nothing directly stopping anybody from porting these apps - they might have to design and implement entire layers of library code first to provide some of the foundations required, but it could be done. However, when the end result is an application that runs slower than running windows 95 in PCx, who is going to bother?