It seems as though Firefox has been slowly decaying over time. I wrote a post on what I loved and hated about Firefox, but it seems as though it is changing - rapidly.
What are the problems: it crashes. Often. Sometimes without warning, the window will just disappear, as though it were never there. Usually it takes me a few seconds to realize what has happened. Other times, it will suddenly stop working (usually while using Gmail) and I have to force close it. This bug appears much more often in Windows than in Ubuntu, but it is still a problem. The other main problem I've seen is that pages are rendered differently on different platforms. Under Windows, sites will look different than under Ubuntu or Mac (I don't know if they are the same under Ubuntu vs. Mac, never had the opportunity to compare side-by-side). Although they are different operating systems, they are the same browser. Get some consistency. Fortunately, the Mac and Linux market share using Firefox combined is under 5%, so we really don't have to care that much. As an Ubuntu user though, I would prefer to see websites appear nicely.
I would have to say that the only reason I'm still using Firefox is due to the amount of extensions. I don't know how I'd do web development without Firebug, at least not nearly as efficiently. There isn't really any other plugins that I would miss that much. In other words, Firebug is the chain attaching me to the lead weight that is Firefox.
What are my alternatives? The first one to come to mind in many people's heads is Internet Explorer. Ha! While it is possible to get IE in Linux, it is slow and ugly - it uses the Wine rendering engine which has never been known for elegance.
Opera is another choice, however it doesn't work on my 64-bit Linux box and not being open-source, I can't compile it. Other than that, I have found it to be fairly usable, with a few things missing: a status bar at the bottom? Is it enable-able? And make an option so that my tabs don't automatically select when I open them. Often when I'm doing my daily blog reading (using Opera under Windows so that I don't have to worry about crashes) I like to open a tab for when I'm done reading the current blog.
The other one I've tried is Epiphany. It is only for GNOME (I remember not thinking much about Konqueror) and so it is not available for platforms other than this - EDIT: apparently it is available for Mac as well. So far, my experience has been good. Although I don't have Firebug, the browser is fast, reliable, and has all the basic features that I use. It uses the Gecko engine, so pages look the same as in Firefox. It even has its own extensions, however the library for this is by far much smaller than that of Firefox.
So it seems that with browsers, it is the same as most other software: there is no silver bullet. I just have to stop complaining and suck it up for when there are problems with something. I'll probably keep complaining though.