Thanks for a very insightful and informative post!
It's interesting to know that you were able to keep flying through with plugins as that sounds like it was one of the issues with all of the updates.
I personally don't use any plug-ins for any browser. I used to use IEPro but with a download manager finally it's becoming less useful. For all of your ad blocking I just wonder if you've ever looked into squid. Stop all of the ads from the server level so you don't have to micromanage all of your pcs and browsers.
For us at work we just won't push out a new browser update unless something is critical that we do. I'm not sure how many desktops you support but there is no way we could keep 500 pcs up to date 24/7 because of some of the software we use. (Have things in place stop changes being made) There is actually a vulnerability in FF 4 - 8 right now that could be used for key logging. It was fixed in FF9 but there is compatibility issues with one of the websites that we use so we can't just upgrade to 9. Since FF is already on 10 I doubt they are going to patch it for any of the older versions, which makes it difficult for us to come up with a solution. Hopefully this version of 10 ESR will start working for the sites we need and we can get on it asap.