Yes, frequent updates, especially those that break plugins, suck massively. Each update is a huge leap of dread into the "well, what's going to break this time" sea.
The biggest single fault I've got with Firerfox (running FF13) isn't updates, it's memory usage. It still leaks massively, and pretty much requires a daily restart. State preservation is good enough that this doesn't matter a whole lot, but the change I'd like to see is one in which a small handful of tabs (I may easily run over 100) are considered "current and active" (foreground, pinned apps), and the rest function more as a stateful bookmark. Which, given that on crash recovery I tend to leave tabs unrefreshed until I actually open them, they largely are.
State-tracking in browsers really sucks. I've begun using the vimperator plugin, and it does a hugely awesome job of helping with this, mostly in the close/undo mode that handles history, and in being able to do partial matches and tab-completion (based on history and bookmarks) when opening new tabs / navigating to a page.
Chrome isn't all that hot. It's fast, it offers a different broken memory model (groups of tabs run in isolated processes, but consume much more memory on a per-tab basis), and it plays well with Google's own Web properties.
But it lacks the extension flexibility Firefox has (especially UI tweaks such as Vimperator, Tree-style Tabs / Tabkit (sadly incompatible with recent releases), and Remove it Permanently) which I find highly useful,
As for updates: call it old age, call it maturity, but I prefer things not change, especially UIs. Much of the greatest frustration and outcry on Linux has been over desktop UI metaphors (GNOME and KDE especially), and Microsoft is rapidly heading into the same fray. As much as I dislike actually using the Mac interface, I have to admit that Apple have kept it highly consistent for the 11 years of OS X. Yes, we can eventually get over it, but big changes should happen very infrequently, and then be left alone for a goodly while. If you need a sandpit to play in, fork a conceptual project, and realize that your userbase for this will be very different from the mainstream, though it may provide some valuable insights.
Frequently interrupting my workflow really, really, really sucks, more than you can possibly imagine. It's one of the joys of running on Debian GNU/Linux -- so long as you're on stable, big changes are infrequent and small changes are all but invisible. Best of both worlds.
IF you are going to rely on a plugin architecture, THEN get the damned baseline worked out and keep it stable. Screwing with APIs pains everyone. It screws your users and your developer community.
I'm becoming of the opinion that we want a bifurcation of the browser. There's an app platform, for Web 2.0 stuff, where it's really necessary. And there's something closer to ePub / Readability / Readability Redux / Instapaper, which presents deep textual content in a format that's both device-appropriate and highly nondistracting. When I find myself using Chrome with the Developer Tools window open, editing page and style elements as I go, something is very, very wrong with the Web.