> you don't know when they are gonna keel over and die
Would it really matter? Browsers are pretty much a commodity item. Of all the big pieces of software in your life, I can't imagine one easier to replace than a browser.
You have to then go through the trouble of redoing persistent logins, transferring bookmarks, history, plugins, etc. That's a nontrivial amount of effort right there.
At least with firefox based browsers I believe the actual user profile folder is pretty compatible across browsers, copying that should copy every aspect of what makes your browser yours, though it might contain extras that won't be utilized by vanilla firefox.
Would it really matter? Browsers are pretty much a commodity item. Of all the big pieces of software in your life, I can't imagine one easier to replace than a browser.