According to mozillaZine Firefox 1.5.0.5 Final is scheduled to be released today (and Thunderbird 1.5.0.5 the day after tomorrow). This will be most likely the last update that version 1.5 will see before the release of version 2.0.
And it seems that this is correct. Everything looks ready for the release.
The Release Notes page is ready. (link)
The release folder is on the FTP and it already has the update versions (link) (Freeware)
View: Firefox 1.5.0.5 Release Notes
News source: mozillaZine