Patch the various recently reported security vulnerabilities in Mozilla.
This is being done instead of the update to 1.0 PR 1 since we're in a ports
freeze, and too many big changes is not a good idea.

This update covers the following Mozilla bugs:

250862
255067
256316

Thanks to nectar for scraping all of these patches together.

Obtained from: Mozilla CVS
Approved by: portmgr (implicit)