Any particular reason you want to use version 1.05? If not, then you can get the latest using synaptic.
One common problem people usually have is that they dont uninstall Firefox first. Dont worry, ALL of your stuff will be safe, including your bookmarks etc. When uninstalling the old version just select remove, NOT completly remove.
When it is finished, look for it again (mozilla-firefox) and then mark for installation. When it is installed you should have a brand spanking new Firefox.
Bookmarks