Stop ubuntu updating thunderbird
It has the latest release, and doesn't disable automatically checking for updates.You also avoid the risk of a third party build adding code from the trunk (code that is not ready for use by everybody yet) without you knowing about it like Ubuntu sometimes does.With Ubuntu (or any Debian based distribution) you can use either the package manager or Automatrix to install the msttcorefonts package .For other distributions (Fedora, open SUSE etc.) you could install the rpm's from this web site if you can't find a more convenient solution.Most Linux distributions have a package manager that supports Thunderbird and Firefox.Many distributions also provide packages for other Mozilla projects (Sea Monkey, Sunbird, ...).
Those RPM software packages are customized versions of the regular releases.Click on the box to the left of it, selecting "Mark for installation". This will install the firefox package plus several other packages it requires. You could also add it to the panel (the equivalent of a windows shortcut), or run it from the terminal.