I use Firefox at home and many other open source tools, but this is a cop-out. Mozilla has been under development long enough that the "beta means never having to say you're sorry" excuse doesn't cut it.
There's a reason most open source tools never leave beta stage or get superceded by newer beta versions. Not having to accept responsibility for a finished product is one of them.
If the FF release had been post-1.0, I'd agree with you, but the FF 1.0 milestone won't show until sometime in the middle to the end of the 4th quarter.
When comparing that to Microsoft's track record of vulnerabilities and fixes (or non-fixes as some might point to), I'd say that Mozilla has a pretty damn good track record.