This sounds like an inept attempt to gather unames and pwords. I'm not seeing it, but I run Linux with Firefox, and very little malware targets this combination.
This thread doesn't contain enough information to figure out the infection and method. It could be cache poisoning that sends your browser to an evil twin with the added code, the Sailnet server could be hacked, or you may have picked up malware on your computer that injects the code into the Sailnet pages as they arrive at your browser.
Regardless of the cause, your part of the clean-up effort is to ensure that your computer is not hacked or infected. I have found that the best defense is a good education coupled with sound practices, so let's talk about sound practice. I'd recommend the following:
1) Flush the browser's cache, delete cookies and otherwise get rid of privacy data, then close it.
Presuming you are running some flavor of Windows, (except for Vista - I have almost no experience with it), you should also:
2) Run an in-depth scan with good antivirus software. No AV software catches everything, but AVG and AVAST are free and are good packages that typically find 95-98% of virii, trojans, and worms and such in objective tests.
3) Download several good anti-malware packages and run them at their most detailed levels. Again, no AM package finds everything, but using several packages improves your kill ratio. Of the free packages, I like Adaware and Spybot Search and Destroy (aka Spybot S&D) best. Adaware is a Lavasoft product. To prevent downloading an evil twin of the same name that will actually install malware instead of removing it, you should always start at Ad-Aware by Lavasoft - Antivirus software, free spyware removal, firewall. It will point you to a clean mirror site. Similarly, Spybot S&D should always be retrieved by starting with its authors at The home of Spybot-S&D!.
4) After you ensure your system is clean, reboot.
5) Make sure your browser of choice is up to date, and minimize your installed browser helpers, tool bars, and other external code.
Other important information:
If you don't mind paying money for your software, you can improve your kill ratio by another percentage point or two by using AV software from either of the two market leaders, McAfee or Norton's.
Why do I say it is your responsibility? Why go to so much trouble? Because every infected machine works against you and against other computers on the Internet. Malware is big business. Criminals and criminal organizations make big money using it. If your computer is infected, it is under someone else's control and can possibly be used to steal your identity, steal money (from you and others), send spam, or attack other computers.
Believe me! The inconvenience of keeping these programs up to date and regularly using them is small in comparison to the downside of financial and identity theft.
I apologize for the length of this post, but you hit a hot topic for me. I have considerable expertise in this area -- part of my job requires that I apply digital forensics to the aftermath in an attempt to figure out what happened, what the damages are, and who is responsible.