985179 - Don't load Experiments.jsm unless service is enabled

Status: RESOLVED WORKSFORME

(Firefox Health Report Graveyard :: Client: Desktop, defect, P4)

Description

[Gregory Szorc [:gps]]

I was looking at how the enabled flag works for Experiments and wanted to point out a performance implication.

By having consulting of the enabled preference in Experiments.jsm, this means you always load Experiments.jsm and derived modules, even if the feature is disabled. This incurs a memory and application load time penalty and makes it more difficult to test the impact of enabling the experiments feature. (We don't do it currently, but in a perfect world we would have automation that enables/disables various Firefox features and attempts to isolate their resource impact.)

A number of features (such as Sync and Firefox Health Report) consult the enabled preferences in the XPCOM service .js file and delay load JSMs until we know the service is enabled.

In practice, this isn't a huge issue because experiments should always be enabled in desktop. But if we need to disable experiments in a channel, it could be problematic, as it will require a new build as opposed to a pref flip to isolate problematic code.

Comment 1

[Georg Fritzsche [:gfritzsche]]

This should have been fixed around bug 993084.