Planète Béranger has raised the ABI issue surrounding Fedora and RHEL’s recent upgrade to Firefox 3. In short, RHEL 5.2 ships with Firefox updated to the new xulrunner-based Firefox 3, but its Eclipse and libswt3-gtk2 is still at 3.2, which depends on the old gtkmozembed interface.
This seems like a good argument in favour of adopting Debian-style package naming, when it comes to libraries: append the ABI version to the (sub)package name containing libraries that are linked to from other packages. So the old Firefox 1.5 would have a libgtkmozembed18 subpackage, that can be shipped with RHEL 5.2 without shipping the rest of Firefox 1.5 (technically speaking, the ABI version is 1.8.x.y, as prior to XULRunner 1.9 the ABI is ever-changing, but packages already handle this by depending on the specific version and release number anyway)
This is already done from time to time in the RHEL/Fedora world, in the form of compatibility packages, but making it the default would avoid this kind of breakage, where a package /has/ to be updated (due to upstream EOL) but parts of it are needed downstream.