We have data on Firefox tab usage. It's not at all what you have suggested. Most Firefox users never have more than 5 or 6 tabs open at a time. The median is about 3 tabs. See http://66.43.220.232/james/mozilla-challenge.html for some slightly out of date but not too far off data. (Note, these are the "geeks" that opted in to our study so it's likely skewed a bit to the heavier tab users.)