Firefox 10 is a long term support-version (like 3.6 was). This will only pull in security fixes. As firefox source tarball grew quite heavily (>70MB), it takes some time to download. Here it needs ~30 minutes. So could it be possible to just distribute a patch for each update? Even if Mozilla does not offer a patch download on their own (like done for the linux-kernel), it should be quite easy to create one. Reproducible: Always
Mozilla team does not have that kind of man power.