Mozilla.org has released an update to Firefox to address several security and stability issues. Taken directly from Firefox's security site:
MFSA 2010-72 Insecure Diffie-Hellman key exchange
MFSA 2010-71 Unsafe library loading vulnerabilities
MFSA 2010-70 SSL wildcard certificate matching IP addresses
MFSA 2010-69 Cross-site information disclosure via modal calls
MFSA 2010-68 XSS in gopher parser when parsing hrefs
MFSA 2010-67 Dangling pointer vulnerability in LookupGetterOrSetter
MFSA 2010-66 Use-after-free error in nsBarProp
MFSA 2010-65 Buffer overflow and memory corruption using document.write
MFSA 2010-64 Miscellaneous memory safety hazards (rv:1.9.2.11/ 1.9.1.14)
Users should apply the update, in addition users should clear their DNS cache and browser storage.