Firefox not ready for the mass market
I love Firefox but customizing to any degree and it becomes obvious that it needs a lot of work before it hits a full version of 1.0. While web page rendering is pretty spot on, there are a number of quirks that would certainly prevent me from recommending it to friends and family. It's the spit and polish of any application that really makes it shine.
My quick list of things that I think would make Firefox a truly spectacular application include:
A solid download manager: Currently (ver 0.8), for downloading plugins and extensions, you can only download one at a time. After that, it misreports what has downloaded and what hasn't and creates redundant dialog boxes. A restart of the application is required. This is a pretty critical one and is surprisingly lacklustre for a public release.
Uninstaller: not for the application itself, but rather for the plugins. Currently it's up to the developers to create an uninstaller but most don't and those that do, their implementations differ from one plugin to the next. A button on the Extensions page (like that on the Themes page) that would uninstall the selected extension would be much easier to use.
Movable Toolbars: Okay, this one is minor compared to the others but with the number of different toolbars that you can install, it would be better if you could move two or more toolbars onto one line. An implementation that would match the ease of use of Internet Explorer with buttons no longer in view still being accessible through a chevron.
With only 0.2 versions left to go, I can't wait for the final release. This is a rock solid browser that has already made it's way into being my default browser.