Nope, it's possible, as long as most of the tabs stay around inactive. (Sadly it doesn't handle too many tabs becoming loaded very well, so if you hit the limit it usually ends with something crashing...)

I can believe it. I have over 2,000 tabs open over the last year. Before the last "clean up", I had 4,000 tabs open. As GP noted, most of them are unloaded (I would say around 3/4). I have 32GB RAM, so firefox issues are a distant memory. (pun intended)

2650 tabs open right now. I'm sure I had more open in the past. No major performance impact. If I click on the "List all tabs" button it takes a second to render the list. The PC is 5 years old, not even close being state of the art.