That's curious. I'm quite used to hearing conversations where people have wildly different performance experiences with Chrome and Firefox. But people with 100s of tabs almost universally say that Firefox handles them ok and Chrome fails miserably.
As for Firefox improvements -- FF7 (September 2011) fixed some big memory problems in the browser, and FF15 (August 2012) prevented a very common kind of leak caused by add-ons. But most of the other releases since FF7 have had minor memory consumption improvements. See https://blog.mozilla.org/nnethercote/category/memshrink/ for more (possibly too much) detail.
If you haven't tried Firefox for over a year and you regularly have 100s of tabs open, you should really try it again. If you have an existing profile, it might be worth using the "reset firefox" feature to make sure it doesn't have a bunch of unnecessary cruft in it -- see http://support.mozilla.org/en-US/kb/reset-firefox-easily-fix....
What is Chrome's bottleneck with hundreds of tabs? The resource load from hundreds of processes? IPC overhead for the browser process to managing the content processes?
Memory usage for that many processes. Even with all the sharing it tries to do, its per-origin (there's usually at most one process for each origin, not for each tab) overhead is much higher than Firefox's.
As for Firefox improvements -- FF7 (September 2011) fixed some big memory problems in the browser, and FF15 (August 2012) prevented a very common kind of leak caused by add-ons. But most of the other releases since FF7 have had minor memory consumption improvements. See https://blog.mozilla.org/nnethercote/category/memshrink/ for more (possibly too much) detail.
If you haven't tried Firefox for over a year and you regularly have 100s of tabs open, you should really try it again. If you have an existing profile, it might be worth using the "reset firefox" feature to make sure it doesn't have a bunch of unnecessary cruft in it -- see http://support.mozilla.org/en-US/kb/reset-firefox-easily-fix....