There have been 2 million downloads of the new Firefox 1.5 since it was released late Tuesday.

Mozilla’s servers weathered the release of Firefox 1.5 much better than last year’s roll-out of 1.0, a Web performance company said Thursday, with the systems showing no evidence of downtime.

Mozilla’s distributed network of mirror sites in 30 countries, said U.K.-based Netcraft, “appears to be handling current download demand with few difficulties.”

Read a review of Firefox 1.5

The developers focused a lot of their efforts on “under the hood” improvements — beyond making the browser super fast, it features much stronger security, a tweaked built-in pop-up blocker to recognize even more sites and controls and several new search sites including Creative Commons, eBay, Amazon.com and Answer.com built into the search bar, and it now supports DHTML.