Firefox 4 for Mobile Beta 5 – Performance Improvements

We just released Firefox 4 for Mobile (Beta 5) and it’s packed with some noticeable improvements. The primary objectives of Beta 5 were improvements in general performance, reducing memory usage and improving rendering while loading and panning the web content. Here are some results to show the progress that’s been made.


We improved application startup speed. We have a system that reports startup time metrics once a day when the application does a check with AMO ( Using this data, we can see the metrics improving from Firefox Mobile Beta 4 to Firefox Mobile Beta 5.

The “First Paint” metric is arguably the most important of the three. That’s when the user should start to see the application appear – not the splash screen, the actual application. Based on the Feb 23rd data, Beta 5 has a nearly 25% improved startup time. The earlier Beta 5 data (Feb 18th) was taken from internal testing and doesn’t represent a large enough population of users and devices. The Feb 23rd data is based almost 2200 data pings and is more comparable to the Beta 4 data, also from Feb 23rd.

Updated: Used actual Beta 5 data and not Beta 5 pre-release data.

Page Loading

We improved page loading performance. We have test suites that measure how long it takes to load a series of static copies of popular websites from a localhost webserver. The test uses static copies, built using wget and some tweaks, to remove the variability of live websites changing over time and network latency issues.

The data shows the exact same test being run on nightly builds of Firefox Mobile, using 3 different Android devices. The SCH-I800 is a Samsung Galaxy Tab. We can see a roughly 21% improvement from Beta 4, beginning of chart, to Beta 5, at the end.


The Mozilla JavaScript team keeps pushing the limits and mobile users get the benefits. We ran some benchmarks on some Android devices using the stock webkit-based browser, Firefox Mobile Beta 3, Firefox Mobile Beta 4 and Firefox Mobile Beta 5.

Go install Firefox 4 Beta 5 for Mobile. Hopefully, you’ll notice the speed improvements too!

13 Replies to “Firefox 4 for Mobile Beta 5 – Performance Improvements”

  1. It is unfortunate that the 3rd party keyboard Swiftkey still crashes with this version of Firefox (and the nightly versions since Beta 5 was released). I’ve pinged them twice on Twitter now (@SwiftKeyApp) and they’ve ignored both messages. Too bad for them. I’ll go back to Swype. =)

  2. @Dietrich – We’re going to keep profiling and try to get whatever wins we can. On most of the devices used by the Mobile team, we load fast enough to ship – much faster than Beta 4. However we still see longer startup times from end users in the field. I’d be happy with another ~10% win myself 🙂

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