I’ve mentioned plugin monitoring, a student project from Seneca College, back when the developers sucessfully got their project “marks”. I am quite pleased to see the project actually land in Firefox 3 (Mozilla 1.9) last week (bug 412770).
Fima (gluon) worked through the review process and landed the monitoring portion of the project. Now, extension developers can use an nsIObserver notification (“experimental-notify-plugin-call”) to monitor the processing time used by a plugin. Fima created an MDC article to cover the details. His blog has many posts on the subject.
He also has a Firefox extension you can use to monitor long running plugin code.