After months of waiting, Mozilla will be releasing the absolutely-we-really-promise final version of Firefox 3.5 tomorrow.

The release, due out last December, has been a long time in coming, after frustrated Firefox users were bombarded with no less than four betas, a preview version and three release candidates.

Originally, Mozilla had planned for the update to its open source Firefox browser to be a smallish, almost incremental one, even dismissively dubbing it 3.1. But the shopping list of features to add and improve became so long, the firm decided to give the version number its proper props.

"The increase in scope represented by TraceMonkey and Private Browsing, plus the sheer volume of work that's gone into everything from video and layout to places and the plugin service make it a larger increment than we believe is reasonable to label '.1'," noted Mozilla engineer Mike Shaver.

Indeed, version 3.5's new TraceMonkey JavaScript engine is said to be a fair bit faster than the original SpiderMonkey in Firefox 3.0, offering a large performance boost by porting code natively into Firefox - in native machine code - executed directly for the processor.

The new version also boasts support for both HTML 5 (with features such as a new video tag) and a private browsing mode - a feature browser rivals Chrome, Safari and IE8 already have.

Private browsing, better known as 'porn mode', ensures a user's Web browsing activities don't leave dirty tell-tale traces behind. That doesn't mean it can keep users anonymous from websites or ISPs, but does mean Firefox itself won't store any data which can be used to trace a user's online activities.

About time too.