I have a shell script that installs all the packages I need on a fresh Ubuntu install, but
1. I only tend to update it after running it and finding that something I was expecting to be installed wasn't (really I should switch to using puppet/cdist/similar for this)
2. I have to set up Firefox manually (downloading extensions etc)
If you're scripting it anyway, you could go one step further and just download all the XPIs to your extension directory, where Firefox will automatically pick them up. I also believe Firefox Sync will be able to sync extensions in the future.
1. I only tend to update it after running it and finding that something I was expecting to be installed wasn't (really I should switch to using puppet/cdist/similar for this)
2. I have to set up Firefox manually (downloading extensions etc)