Halfway joking here but I think perfectly ordinary people who just use a few tabs at a time tends to just use whatever thay get their hands on, -IE on Windows or Safari on Mac.
This means there is already a bias here: Those who use FF use it anyway because there is no alternative that has Scrapbook extension (offline browsing w/searchability), tree tabs (for automatic mind mapping) that also handles 100-200 tabs in a good way. (Read up on David Allen on using your memory for real work not to remember addresses and tasks for why some people find this useful.)
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 See http://126.96.36.199/james/mozilla-challenge.html for some slightly out of date but not too far off data.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.)