Firefox 1.5.0.7 have just been released with many Improvements to product stability and Several security fixes including bugs :
MFSA 2006-64 Crashes with evidence of memory corruption (rv:1.8.0.7)
MFSA 2006-62 Popup-blocker cross-site scripting (XSS)
MFSA 2006-61 Frame spoofing using document.open()
MFSA 2006-60 RSA Signature Forgery
MFSA 2006-59 Concurrency-related vulnerability
MFSA 2006-58 Auto-Update compromise through DNS and SSL spoofing
MFSA 2006-57 JavaScript Regular Expression Heap Corruption
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It’s highly recommanded to upgrade to this new version, if Firefox didn’t upgrade automaticly yet.