I used AdminStudio to package Fx2 as an MSI. Deploys great, with one minor issue. The included js3250.dll file is always versioned at 220.127.116.11, no matter which Mozilla build (or product!) you're working with. So, to get the MSI to update an existing installation, you must set that file to "Copy Always."
I don't believe that lastmod is a hash that prevents you from altering the whitelist. It's just a modification date value. As long as you have a valid value then Google should still use the modified whitelist.
A ready-to-go sequenced package for SoftGrid is avaiable at instantapp.net.
For Re-Packaging Firefox, you can follow this link:
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