You want to disable Java due to the Flashback attacks going on, but not disable Javascript.
You get that error when a Javascript is taking too long to execute, (can be many reasons), for now just Cancel there.
If you have a PPC Mac you're still reasonably safe, but if an IntelMac see...
Disable Java in your Browser settings, not JavaScript.
Flashback - Detect and remove the uprising Mac OS X Trojan...
http://www.mac-and-i.net/2012/04/flashback-detect-and-remove-uprising.html
In order to avoid detection, the installer will first look for the presence of some antivirus tools and other utilities that might be present on a power user's system, which according to F-Secure include the following:
/Library/Little Snitch
/Developer/Applications/Xcode.app/Contents/MacOS/Xcode
/Applications/VirusBarrier X6.app
/Applications/iAntiVirus/iAntiVirus.app
/Applications/avast!.app
/Applications/ClamXav.app
/Applications/HTTPScoop.app
/Applications/Packet Peeper.app
If these tools are found, then the malware deletes itself in an attempt to prevent detection by those who have the means and capability to do so. Many malware programs use this behavior, as was seen in others such as the Tsunami malware bot.
http://reviews.cnet.com/8301-13727_7-57410096-263/how-to-remove-the-flashback-ma lware-from-os-x/
http://x704.net/bbs/viewtopic.php?f=8&t=5844&p=70660#p70660
The most current flashback removal instructions are F-Secure's Trojan-Downloader:OSX/Flashback.K.