Mac OS X 10.5.3 may have fixed over 200 bugs in Leopard, but it appears to be causing some significant new ones for users of various Mozilla products.

Mozilla's developers have traced the problem back to an Apple bundle called VerifiedDownloadPlugin that was initially introduced in Mac OS X 10.4.7 and is thought to be part of a Dashboard widget validation system of some kind. As a result of changes made by Apple in 10.5.3, dynamically loading this library can cause the system to hang or crash. Songbird product manager Daniel Raffel has already informed Apple's senior vice president of software engineering, who says that Apple is investigating the issue.

A workaround patch that effectively solves the problem for Mozilla-based products was developed yesterday by Steven Michaud, a Firefox developer who is known for his work on the JEP. "As you can see in my patch's comments, it gets around the Apple bug (that, as of OS X 10.5.3, you can't dlopen the VerifiedDownloadPlugin) by using nlist() to check for a symbol first, to see if dlopen() should be used on a given plugin," Michaud wrote.

He has made available a Mac OS X Firefox build with the patch applied so that developers can test the solution and make sure that it works properly. Several testers have reported that his fix seems to do the trick. He intends to request that the bug be marked as a blocker for Gecko 1.9 so that it can be included in final release of Firefox 3. That would also require Mozilla to issue a third release candidate.

There are some concerns that the dynamic loading problem might not be isolated to the VerifiedDownloadPlugin bundle, which means that there could be a more serious problem in Apple's platform caused by the 10.5.3 release. Apple has not yet provided details about the scope of the problem or how it is being addressed.

Update: Mozilla has released a third Firefox 3 release candidate which contains the workaround patch that resolves the problem.