Neil Turner's Blog

Blogging about technology and randomness since 2002

Firefox 4 – behind the scenes changes on OS X

Red Panda
I was going to post about all the awesome changes due in Firefox 4 on Mac OS X, but Mozilla developer Josh Aas has done it better already. I’ll therefore just summarise a few of the changes.
Firefox 4 Beta 7 is due out imminently. The user interface changes aren’t as far reaching on OS X as they are on Windows Vista and 7, although there are a few differences (tabs on top, status bar gone, a combined stop/refresh/go button in the address bar). The main changes are behind the scenes.
First of all, if you have Snow Leopard and a Mac with a 64-bit processor, then Firefox will run as a 64-bit process. Normally switching to 64-bit shouldn’t offer a major boost to performance but tests suggest that Firefox starts up around 25% faster, largely due to caching of shared libraries. There’s also the cross-platform speed improvements courtesy of the improved JavaScript engine, which now runs the SunSpider test suite faster than developer builds of Google Chrome (although the difference is measured in milliseconds so it’s probably not noticeable to most users).
Out-of-process plugin support is also new, having previously only been available on Windows and Linux. This boosts stability: if the plugin crashes, it shouldn’t crash the browser as well; but should also facilitate parallel processing on multi-core CPUs (which many are these days, especially on the Mac). On 64-bit machines it offers the additional benefit of being able to host 32-bit plugins; most popular plugins, including Adobe Flash, aren’t widely available as 64-bit yet.
There is a price for all of these improvements – as far as I can tell PowerPC Macs are no longer supported, and you will need a minimum of Leopard (10.5) to run Firefox 4; Tiger (10.4) support is no longer offered. If this applies to you, you’ll have to stick with Firefox 3.6. You’ll also have to update all of your extensions as the vast majority will need to be rewritten for Firefox 4; but on the plus side a number can be installed without needing to restart the browser.
I’m writing this post from a candidate build for Firefox 4 Beta 7, and have to say I’m impressed with the changes. It’s definitely faster than 3.6 and the out-of-process plugin support is great – it’s much nicer seeing a sad Lego brick when Flash crashes than the whole browser disappearing. When the final beta comes out, I’d recommend downloading it.


  1. I’m still on 3.6.1. I *was* waiting for the final, non-beta, non-rc release, but they can’t stop pushing back the release date, and the beta sounds stable enough. Once beta7 is out (reported to be a feature freeze release), i’ll bite.
    Looking forward to faster speed, less freezes/crashes, and bookmarks/gmail in tabs!

  2. I think b7 is the version that I’ll end up installing. Like Carl I was waiting for something a bit more release candidatey before installing but this sounds too good to pass up.