Barring any last-minute surprises, the Firefox Web browser on Tuesday will turn 1.0.

Although the release is technically a preview, the 1.0 version is a significant milestone for the free open-source browser software, which has already won an enthusiastic following as an alternative to Microsoft’s Internet Explorer.

“Today’s builds are the new candidate 1.0PR (preview release) builds,” Asa Dotzler, the Mozilla Foundation’s community quality advocate, wrote in a Web log posting Saturday night. “If all goes well with these builds, they’ll become the official Firefox 1.0 Preview Release builds on Tuesday morning.”

Spun off last summer by AOL Time Warner, the Mozilla Foundation is the open-source group that produces both Firefox and its predecessor, the Mozilla browser.