When I am installing Mozilla Firebird I get :

root@linux:~# tar -zxvf MozillaFirebird-0.6-i686-pc-linux-gnu.tar.gz
MozillaFirebird/
MozillaFirebird/chrome/
MozillaFirebird/chrome/en-US/
MozillaFirebird/chrome/en-US/locale/
MozillaFirebird/chrome/en-US/locale/en-US/
MozillaFirebird/chrome/en-US/locale/en-US/global/
MozillaFirebird/chrome/en-US/locale/en-US/necko/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/security/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/layout/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/dom/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/profile/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/directory/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/history/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/pref/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/search/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/sidebar/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/xpinstall/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/wallet/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/timebomb/
MozillaFirebird/chrome/en-US/locale/en-US/communicator/webservices/
MozillaFirebird/chrome/en-US/locale/en-US/navigator/
MozillaFirebird/chrome/en-US/locale/en-US/cookie/
MozillaFirebird/chrome/en-US/locale/en-US/wallet/
MozillaFirebird/chrome/en-US/locale/en-US/p3p/
MozillaFirebird/chrome/en-US/locale/en-US/autoconfig/
MozillaFirebird/chrome/en-US/locale/en-US/pipnss/
MozillaFirebird/chrome/en-US/locale/en-US/pippki/
MozillaFirebird/chrome/en-US/locale/en-US/browser/
MozillaFirebird/chrome/en-US/locale/en-US/browser/bookmarks/
MozillaFirebird/chrome/en-US/locale/en-US/browser/downloads/
MozillaFirebird/chrome/en-US/locale/en-US/browser/history/
MozillaFirebird/chrome/en-US/locale/en-US/browser/pref/
MozillaFirebird/chrome/comm/
MozillaFirebird/chrome/comm/content/
MozillaFirebird/chrome/comm/content/necko/
MozillaFirebird/chrome/comm/content/communicator/
MozillaFirebird/chrome/comm/content/communicator/xml/
MozillaFirebird/chrome/comm/content/communicator/profile/
MozillaFirebird/chrome/comm/content/communicator/pref/
MozillaFirebird/chrome/comm/content/communicator/directory/
MozillaFirebird/chrome/comm/content/communicator/history/
MozillaFirebird/chrome/comm/content/communicator/related/
MozillaFirebird/chrome/comm/content/communicator/search/
MozillaFirebird/chrome/comm/content/communicator/sidebar/
MozillaFirebird/chrome/comm/content/communicator/timebomb/
MozillaFirebird/chrome/comm/content/communicator/alerts/
MozillaFirebird/chrome/comm/content/communicator/xpinstall/
MozillaFirebird/chrome/comm/content/communicator/wallet/
MozillaFirebird/chrome/comm/content/communicator/p3p/
MozillaFirebird/chrome/comm/content/xbl-marquee/
MozillaFirebird/chrome/comm/content/navigator-platform/
MozillaFirebird/chrome/comm/content/navigator/
MozillaFirebird/chrome/comm/content/navigator-region/
MozillaFirebird/chrome/comm/content/communicator-platform/
MozillaFirebird/chrome/comm/content/communicator-region/
MozillaFirebird/chrome/comm/content/cookie/
MozillaFirebird/chrome/comm/content/wallet/
MozillaFirebird/chrome/comm/content/p3p/
MozillaFirebird/chrome/comm/content/autoconfig/
MozillaFirebird/chrome/toolkit/
MozillaFirebird/chrome/toolkit/content/
MozillaFirebird/chrome/toolkit/content/global/
MozillaFirebird/chrome/toolkit/content/global/widgets/
MozillaFirebird/chrome/toolkit/content/global/bindings/
MozillaFirebird/chrome/toolkit/content/global-platform/
MozillaFirebird/chrome/toolkit/content/global-region/
MozillaFirebird/chrome/en-US.jar
MozillaFirebird/chrome/chromelist.txt
MozillaFirebird/chrome/classic/
MozillaFirebird/chrome/classic/skin/
MozillaFirebird/chrome/classic/skin/classic/
MozillaFirebird/chrome/classic/skin/classic/global/
MozillaFirebird/chrome/classic/skin/classic/global/filepicker/
MozillaFirebird/chrome/classic/skin/classic/global/arrow/
MozillaFirebird/chrome/classic/skin/classic/global/console/
MozillaFirebird/chrome/classic/skin/classic/global/toolbar/
MozillaFirebird/chrome/classic/skin/classic/global/splitter/
MozillaFirebird/chrome/classic/skin/classic/global/icons/
MozillaFirebird/chrome/classic/skin/classic/global/checkbox/
MozillaFirebird/chrome/classic/skin/classic/global/radio/
MozillaFirebird/chrome/classic/skin/classic/global/menu/
MozillaFirebird/chrome/classic/skin/classic/global/scrollbar/
MozillaFirebird/chrome/classic/skin/classic/global/scrollbar/slider/
MozillaFirebird/chrome/classic/skin/classic/global/tree/
MozillaFirebird/chrome/classic/skin/classic/global/progressmeter/
MozillaFirebird/chrome/classic/skin/classic/communicator/
MozillaFirebird/chrome/classic/skin/classic/communicator/cookie/
MozillaFirebird/chrome/classic/skin/classic/communicator/bookmarks/
MozillaFirebird/chrome/classic/skin/classic/communicator/directory/
MozillaFirebird/chrome/classic/skin/classic/communicator/profile/
MozillaFirebird/chrome/classic/skin/classic/communicator/related/
MozillaFirebird/chrome/classic/skin/classic/communicator/search/
MozillaFirebird/chrome/classic/skin/classic/communicator/sidebar/
MozillaFirebird/chrome/classic/skin/classic/communicator/xpinstall/
MozillaFirebird/chrome/classic/skin/classic/communicator/brand/
MozillaFirebird/chrome/classic/skin/classic/communicator/icons/
MozillaFirebird/chrome/classic/skin/classic/communicator/taskbar/
MozillaFirebird/chrome/classic/skin/classic/communicator/alerts/
MozillaFirebird/chrome/classic/skin/classic/editor/
MozillaFirebird/chrome/classic/skin/classic/editor/icons/
MozillaFirebird/chrome/classic/skin/classic/messenger/
MozillaFirebird/chrome/classic/skin/classic/messenger/icons/
MozillaFirebird/chrome/classic/skin/classic/messenger/addressbook/
MozillaFirebird/chrome/classic/skin/classic/messenger/addressbook/icons/
MozillaFirebird/chrome/classic/skin/classic/messenger/messengercompose/
MozillaFirebird/chrome/classic/skin/classic/messenger/smime/
MozillaFirebird/chrome/classic/skin/classic/messenger/smime/icons/
MozillaFirebird/chrome/classic/skin/classic/navigator/
MozillaFirebird/chrome/classic/skin/classic/navigator/btn1/
MozillaFirebird/chrome/classic/skin/classic/navigator/icons/
MozillaFirebird/chrome/classic/skin/classic/browser/
MozillaFirebird/chrome/classic/skin/classic/browser/bookmarks/
MozillaFirebird/chrome/classic/skin/classic/browser/downloads/
MozillaFirebird/chrome/classic/skin/classic/browser/pref/
MozillaFirebird/chrome/comm.jar
MozillaFirebird/chrome/installed-chrome.txt
MozillaFirebird/chrome/embed-sample/
MozillaFirebird/chrome/embed-sample/content/
MozillaFirebird/chrome/embed-sample/content/embed/
MozillaFirebird/chrome/embed-sample/locale/
MozillaFirebird/chrome/embed-sample/locale/en-US/
MozillaFirebird/chrome/embed-sample/locale/en-US/embed/
MozillaFirebird/chrome/embed-sample/skin/
MozillaFirebird/chrome/embed-sample/skin/classic/
MozillaFirebird/chrome/embed-sample/skin/classic/embed/
MozillaFirebird/chrome/toolkit.jar
MozillaFirebird/chrome/en-win/
MozillaFirebird/chrome/en-win/locale/
MozillaFirebird/chrome/en-win/locale/en-US/
MozillaFirebird/chrome/en-win/locale/en-US/global-platform/
MozillaFirebird/chrome/en-win/locale/en-US/navigator-platform/
MozillaFirebird/chrome/en-win/locale/en-US/communicator-platform/
MozillaFirebird/chrome/en-win/locale/en-US/communicator-platform/pref/
MozillaFirebird/chrome/embed-sample.jar
MozillaFirebird/chrome/en-unix/
MozillaFirebird/chrome/en-unix/locale/
MozillaFirebird/chrome/en-unix/locale/en-US/
MozillaFirebird/chrome/en-unix/locale/en-US/global-platform/
MozillaFirebird/chrome/en-unix/locale/en-US/navigator-platform/
MozillaFirebird/chrome/en-unix/locale/en-US/communicator-platform/
MozillaFirebird/chrome/en-unix/locale/en-US/communicator-platform/pref/
MozillaFirebird/chrome/classic.jar
MozillaFirebird/chrome/en-mac/
MozillaFirebird/chrome/en-mac/locale/
MozillaFirebird/chrome/en-mac/locale/en-US/
MozillaFirebird/chrome/en-mac/locale/en-US/global-platform/
MozillaFirebird/chrome/en-mac/locale/en-US/navigator-platform/
MozillaFirebird/chrome/en-mac/locale/en-US/communicator-platform/
MozillaFirebird/chrome/en-mac/locale/en-US/communicator-platform/pref/
MozillaFirebird/chrome/en-win.jar
MozillaFirebird/chrome/US/
MozillaFirebird/chrome/US/locale/
MozillaFirebird/chrome/US/locale/US/
MozillaFirebird/chrome/US/locale/US/navigator-region/
MozillaFirebird/chrome/US/locale/US/communicator-region/
MozillaFirebird/chrome/US/locale/US/communicator-region/wallet/
MozillaFirebird/chrome/US/locale/US/global-region/
MozillaFirebird/chrome/US/locale/US/browser-region/
MozillaFirebird/chrome/en-unix.jar
MozillaFirebird/chrome/modern/
MozillaFirebird/chrome/modern/skin/
MozillaFirebird/chrome/modern/skin/modern/
MozillaFirebird/chrome/modern/skin/modern/communicator/
MozillaFirebird/chrome/modern/skin/modern/communicator/cookie/
MozillaFirebird/chrome/en-mac.jar
MozillaFirebird/chrome/pipnss/
MozillaFirebird/chrome/pipnss/content/
MozillaFirebird/chrome/pipnss/content/pipnss/
MozillaFirebird/chrome/US.jar
MozillaFirebird/chrome/pippki/
MozillaFirebird/chrome/pippki/content/
MozillaFirebird/chrome/pippki/content/pippki/
MozillaFirebird/chrome/modern.jar
MozillaFirebird/chrome/browser/
MozillaFirebird/chrome/browser/content/
MozillaFirebird/chrome/browser/content/browser/
MozillaFirebird/chrome/browser/content/browser/bookmarks/
MozillaFirebird/chrome/browser/content/browser/downloads/
MozillaFirebird/chrome/browser/content/browser/history/
MozillaFirebird/chrome/browser/content/browser/pref/
MozillaFirebird/chrome/pipnss.jar
MozillaFirebird/chrome/overlayinfo/
MozillaFirebird/chrome/overlayinfo/communicator/
MozillaFirebird/chrome/overlayinfo/communicator/content/
MozillaFirebird/chrome/overlayinfo/communicator/content/overlays.rdf
MozillaFirebird/chrome/overlayinfo/navigator/
MozillaFirebird/chrome/overlayinfo/navigator/content/
MozillaFirebird/chrome/overlayinfo/navigator/content/overlays.rdf
MozillaFirebird/chrome/overlayinfo/messenger/
MozillaFirebird/chrome/overlayinfo/messenger/content/
MozillaFirebird/chrome/overlayinfo/messenger/content/overlays.rdf
MozillaFirebird/chrome/overlayinfo/browser/
MozillaFirebird/chrome/overlayinfo/browser/content/
MozillaFirebird/chrome/overlayinfo/browser/content/overlays.rdf
MozillaFirebird/chrome/pippki.jar
MozillaFirebird/chrome/browser.jar

gzip: stdin: unexpected end of file
tar: Unexpected EOF in archive
tar: Unexpected EOF in archive
tar: Error is not recoverable: exiting now

What should I fix?

did you just do tar zxvf mozillafirebird.tar.gz
?

Bad download... 95% chance the tar file is corrupt. Try to download it again.

didn't even think of that one...