Firefox stats all registered plugins on the main thread early during startup, adding >100ms to startup time and delaying first paint.

How early? This should typically be done lazily when the first web page requests a plugin.

Is this possibly triggered by the addon-manager during startup?

(In reply to Georg Fritzsche [:gfritzsche] from comment #2) > Is this possibly triggered by the addon-manager during startup? By default the add-ons manager shouldn't request this until about:addons opens or some other code requests it like an add-on or something like FHR that might report plugin info. A stacktrace of the request would be useful here.

It turns out PDF.js initialization (bug 881575) + querying the MIME-type of .jsm files (bug 881578) were triggering plugin list initialization (In reply to Benjamin Smedberg [:bsmedberg] from comment #1) > How early? This should typically be done lazily when the first web page > requests a plugin. Before first paint (In reply to Georg Fritzsche [:gfritzsche] from comment #2) > Is this possibly triggered by the addon-manager during startup? What :Mossop said :)