Lightly?
Understanding that the phrase; "To each his/her own" strictly applies here, having 193 (200, 300, 400, any-number-above-100) tabs open in Firefox in my experience (more than several years) would be considered more than excessive by most Firefox users and not the "norm" so to speak. That being said, I'm rather amazed myself that Firefox would be stable with that many tabs open. Of course, a lot depends on the hardware Firefox happens to be running on. Attempting to run Firefox on a dual core (name your flavor) with 2 GB (with 32-bit OS) to 4 GBs (with 64-bit OS) of memory, you'll be lucky to keep 20 to 30 tabs open without choking. Get up into the quad core and 8+ GB of memory and now you have the kind of serious horsepower to run any browser with 100 or more tabs open.
It's not so much the browser these days but the WWW itself that requires a rather large amount of power hardware-wise in order to browse without problems. The days of static HTML based sites are long over. Now it's all Flash (apps and video), Java, javascript, HTML 5, PHP, etc, etc. It's a safe bet that nearly all sites use a combination of 2 or more of these.
