It was so bad that I had to close firefox when I wanted to do anything else. If I played a full screen game it would work great for about half an hour the suddenly it'd chug along at 10fps. Without fail the issue was Firefox deciding to consume 90% CPU. And again this is without installing a single add-on ever.
It may be better today. I don't know. I don't care. I switched to Chrome and haven't looked back since.
State recovery is quite good for the most part, even if memory use is somewhat pants.
And then years later they have the "MemShrink project". Which basically was admitting that they were spouting bullshit about it being addons for years.
This isn't to say Chrome doesn't have its own memory or performance problems. GMail for example will eat up to 1GB of memory eventually before I notice I'm low. I have to actually close the tab (reloading doesn't fix it) and re-open it. It's "only" using 500MB right now...
Any organization that can live in denial for years and years about the core issue with their product is going to die. Mozilla is tightly connected to the web developer community, but has a complete disconnect from the problems facing its actual users. When Firefox shipped, it was a great, light-weight alternative to Mozilla. From my point of view as a user, I haven't seen any substantial improvements since 1.0 shipped in 2004 -- spell check is nice, and given how often it crashes, restoring tabs when the browser is opened is nice -- but that's all. Otherwise, if not for security issues and web site compatibility issues, I'd be on Firefox 1.0 (which worked fine on sub-GHz machines).
Aside from that, virtually all development effort has been aimed at making a better IDE for web developers. I guess that benefits me since, ultimately, I can visit nicer web sites in Chrome.
Which is expected, because why would you stay if you were really bothered?
Comments from an active user, though... I've stuck with Firefox out of habit probably more than anything else, but now most of the things people (including me) were complaining about are already gone -- as of the last update, Firefox with -- sheesh, I guess I have about 100 tabs in 2 windows -- takes up under 500MB after using it all day, and in the morning it starts in a few seconds (they don't force-reload all your open tabs on startup anymore, just the active ones and I think text from the others is cached locally).
Chrome becomes unusable if I try to use it like a to-do list like this, for UI as well as memory reasons; not that I could say easily how much memory Chrome is using at the moment, with 20 tabs; the separate processes defeats seeing that easily, alas (there must a simple way to check, but I haven't tried).
It's quite stable, and even when it was still crashier (last year?) it's been years since I've actually lost my tabs after a crash; they've always been auto-recovered (and it has that nice prompt to let me close the ones I think may be causing trouble before relaunching).
Given different usage patterns, etc., I have no idea if people trying the actual, current FF will want to go back -- but for anyone who left more than a few months ago (especially if you left due to memory footprint) I'd suggest trying it again sometime.
[And I like the more frequent releases, personally -- I always hated the slow release cycle, and feel like they're starting to get into the swing of it now -- but I obviously don't speak for the crowd on this one...]
The equivalents on Chrome are simply not good enough. I don't know if this is an issue with all Chrome extensions, but Wet Banana / Scrollbar Anywhere on it seem to be running in a low priority and thus have sub-par performance. Scrolling is choppy and doesn't always even initiate, depending on where on the page I right-clicked.