An updated InWorldz viewer (184.108.40.206479) is now available. It includes all the fixes and improvements present in the official SL viewer up to SL 5.0.6, as well as the previous InWorldz customizations to make the SL viewer more acceptable to InWorldz residents. It also includes changes to the text fonts used, to make the text sharper and crisper and easier to read. (Thanks Benski for showing the side-by-side comparison of Firestorm and InWorldz fonts.) More detailed release notes and the Linux version will follow, but in the meantime we wanted to make these viewers available for use.
The Linux installer should be available within a few days. In the meantime, these viewers are complete and are already available from the download page and the Viewers page on the wiki:
These viewer installers are also available via the inworldz.com Downloads page, which will auto-detect the most approproate viewer for your operating system.