Sadly I can't vote in your poll as none of the answers really suit how I feel about Firefox. I shall endeavour to elaborate
I think as Firefox gains popularity, more and more bugs will be discovered. Many of these will be small, and some like recently will be quite critical and require immediate fixes.
The latest bug fixes were made before any code was written to exploit it. And such bugs are fixed fairly rapidly and distributed accordingly. The question is, should we worry that the Firefox developers are keeping us safe, albeit by releasing new versions within a relatively small space of time? I am happy to download new versions when they are released. People on slow connections might not be so willing to do so however.
Your point about Firefox being a beta (or preview as Mozilla like to call it) is quite an interesting one. On the one hand you could argue that since Firefox hasn't yet reached version 1, update and bugs are to be expected. On the other hand, you will find people that will argue that major flaws should be less frequent as we get closer to a final release version.
People will always compare Firefox to IE, which is not surprising considering IE is what most people are "switching" from. IE is currently in its sixth revision, so there has been far more time to refine it and fix bugs and security flaws. Does Firefox benefit from security from obscurity? Is it less popular and thus less subject to attacks? Will we see a vast number of new bugs as Firefox grows in popularity? To be honest I think not. In any large piece of software, you will get bugs, and things people are not happy with. A web browser is a huge piece of technology, even though it can seem simple to some people. I think the Firefox developers are doing a great job.
Firefox is doing what Opera, Netscape and even Mozilla haven't done. And that is to seriously start to threaten IE's dominance on the global stage. The amount of press that Firefox gets is untrue for something yet to hit version 1.0
We can have all the ifs and buts, but lets look at the now. Currently I would say Firefox is more secure than IE. Currently. Currently Firefox outstrips IE for features that I find genuinely useful. Anyone who uses Firefox as their main browser does not like going back to IE. I sure don't! In short, at this current point in time, Firefox is easily the best browser currently available for me personally.
Finally I would say not to worry. Bug will be found, bugs will be fixed. Its that simple. If in future things change, then things change, lets not get over excited about it. Heck, just over 18 months ago, I had never even heard of Firefox (probably because it was called Firebird back then
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