Dietrich blogged a “wake up and smell the startup” executive overview of startup issues caused by our extension practices. This post is a “numbers” followup. For this experiment I installed a brand-spankin-new copy of Linux Firefox 3.6. Firefox is installed on a 7200 hard drive, the rest of my system lives on an SSD. The CPU is core2duo, keep in mind these numbers will be significantly worse for people running on netbooks and other common hardware. The numbers vary +/- 150ms, but the general picture is pretty clear.
|Firefox 3.6 with no extensions:||2240ms|
|+Adblock Plus (no subscriptions)||2538ms|
|+Video Download Helper||2727ms|
|+EasyList subscription for adblock||4044ms|
I just doubled cold startup time for Firefox by merely adding 4 extensions. It takes weeks or even months of developer time to shave off every 100ms off Firefox startup, but mere seconds to undo any of those gains by installing extensions. These are just the top-4 extensions in the list (presumably they are higher quality too), I’m sure there are lots of other extensions with more drastic performance hits.
Dietrich’s post details some of the remedies that should reduce the startup cost of extensions. For the inquisitive minds: I used SystemTap to produce a report of files read by Firefox on startup ordered by their startup cost.
Dietrich asked me to summarize warm startup too:
- Without extensions: 550ms
- With above Extensions: 1800ms
Note that this is a developer blog, so by “remedies” I meant “things developers can do to”. There is little normal users can do short of complaining to the extension authors.
This post isn’t meant to shame specific extension authors into speeding up their extensions. The aim is to show that a measurable percentage of startup is due to extensions and that we need to:
- Educate extension developers about it
- Provide better tools to measure slowdowns caused by extensions
- Make sure that the Firefox side of extension handling is sufficiently efficient