FireFox 2 is released and can be downloaded at GetFireFox.com! What does this mean for us browser compatibility testers?

From experience, my compatibility testing woes that come with version changes are:

1. JavaScript version changes, causing JavaScript errors.
2. Rendering engine changes (especially CSS); causing display issues (e.g. object alignment, font changes/inconsistency).

So....as I peruse the FireFox 2 feature list I see an upgrade to JavaScript 1.7. Hmm, sounds historically defect prone...BUT, before I read the feature list I went and did my own homework of seeing if the JavaScript version changed. My homework unveiled that FireFox 2 was using JavaScript 1.5? WHAT THE? Am I looking at an issue caused by having multiple FireFox installations on a machine (I have 1.0.8, 1.5.4, and 2.0 installed). When you're running FireFox 2 what is your JavaScriptVer when you visit BrowserHawk.com? Leave your findings in the comments please!