really? I have about 20 tabs open on Chrome now with no lag, with one tab open in Firefox my whole system grinds to a halt.
My experience is that performance on Chrome degrades beyond 30 or 40 tabs, though the exact value depends on your system.
You can have Firefox open with 400 tabs without too much performance degradation. Many tabs will be swapped to disk or not even loaded, but the tabs you actually use will work just fine.
(also, Firefox on Mac seems to perform less smoothly than on other platforms, though I'm not entirely sure why)
For me it's much sooner... on my work machine with limited memory, firefox is almost always noticeably better after 3-4 tabs, or even fewer when they're memory-hungry sites like gmail. With only 1GB on that machine, I tend to be hyper-sensitive to memory usage, and unfortunately chrome tends to basically use up all memory on the system once I reach 8-9 tabs. FF gets a fair bit further.
The upside of chrome on that machine, however, is that the process-per-tab thing makes much easier to control memory usage: although tabs chew up memory quickly, closing a tab gives you back all the memory it was using, whereas with FF the relationship between closing tabs and giving memory back to the system is much fuzzier....
Firefox currently uses about 3GB memory, which means I have plenty of memory left on my computer. So I do not think memory usage in the general case is so bad for Firefox and neither is scalability or performance. The problem Firefox historically has had and still to a degree has is lack of responsiveness.
I hit the 3GB limit pretty much daily, FF crashes, I start it up again, back come my 200 tabs, thankfully not all loaded at once!
I'll admit I know the cause of the problem, Reddit Enhancement Suite, but I'd rather have FF crash daily than go without RES.
You can't possibly have your attention spread over a hundred sites at a time. Are you using them as bookmarks?