kaled - 12:36 am on May 18, 2010 (gmt 0)
I run Firefox in a pretty minimal configuration. The only non-standard additions are a dictionary and flashblock yet I have seen memory leaks and pauses many times.
I presume that all extensions allocate memory through Firefox rather than directly through the Windows API, this being the case, if an extension were to blame, basic debugging would find the culprit. Mozilla may be comfortable blaming others but, one way or another, the memory leak is their responsibility and it's been around for ages.
As for the pause bug, it is clear that a task that should be assigned to an idle-priority thread is running in the main thread - that's a rookie mistake that could be fixed in a few minutes.