Mozilla have released Firefox 4 Beta 1 to the public, after final beta 1 builds started to appear last week.

Firefox 4 has many changes over 3.6, and is based on Gecko 2.0 rendering engine. New in Firefox 4 include:

• Tabs on top for Windows by default  (Mac and Linux changes coming later)
• Menu bar replaced by Firefox button for Windows Vista and Windows 7 users
• New add-ons manager
• CSS transitions
• Native HD HTML5 WebM video support

A full list of changes can be found in the release notes. Firefox users can download Firefox 4 Beta 1 from the Firefox Beta website.

Opera has just released Opera 10.60 Beta 1, almost two weeks after releasing an alpha.

New in this beta is geolocation services, offline web application support, web workers, and the new WebM video support. The browser is also up to 75% faster than Opera 10.50.

A full list of changes can be read in the changelog, while the beta browser can be downloaded from the Opera Next website.

Firefox 4 nightly releases now include built-in support for WebM video, based on Google’s open VP8 codec.

WebM support is included in Windows, Mac, and Linux Firefox nightly builds. Previously, WebM had been made available by special builds that were announced with the release of the WebM format.

Firefox Programmer Chirs Pearce has posted details on his blog for users wanting to build the browser themselves.

Eager testers can download Firefox 4 Alpha from the Firefox nightlies. Firefox 4 final is expected before the end of the year.