> Why would you want so many tabs open in the first place?

Some reasons:

- Ctrl-clicking to open tabs since I can then load them in the background (because I'm impatient, and because I don't want to get distracted by clicking into all the references in the main tab while reading.

- using tab tree extension I can then easily see what path lead to some interesting page I found

- by default, if you type ab address you already have open in another tab, Firefox will jump to that tab.

> Is this really a common way to use a browser?

Yep. Bot extremely common but I do it and a number of other HN-ers as well. Mozilla seems to be aware of it and seems to have it in their performance tests or something.

My workflow is the same. I'll usually have 100 tabs open on a particular device, going up to nearly 1000 tabs across my phone, laptop, and desktop in rare instances.