From MozillaZine Knowledge Base

This is a compilation of issues with Firefox that have are unique to or are more likely to happen with Windows Vista.

• Windows Media Player missing plugin alerts - Install the new Windows Media Player Firefox Plugin [1]
• "The program must close to allow a previous installation attempt to complete. Please restart." or an error message referencing "xpicleanup.dat"
• "Error opening file for writing..."
• Applications open IE on Vista
• Can't set default browser - update to Firefox 2.0.0.2 or later
• Window shakes - update to Firefox 2.0.0.4 or later