Yes, my recollection of the Squeak browser plugin was that the performance was indistinguishable from running regular Squeak, several orders of magnitude better than SqueakJS. And the startup time was vastly better than any Java plugin code.

However, if you were on dial-up, and your browser didn't already have a cached copy of the smalltalk image, then you were in for a quite a wait. (Though no doubt this could have been addressed - there were people arguing at the time for the creation of a much smaller Squeak image, but a combination of the lack of a clear goal to motivate this work, and the fact that for most existing users it was a non-issue, meant that nothing came of this within the timeframe where it might have made a difference.)

But it may be that this is all moot, because it could be argued that any browser-plugin deployment model would ultimately fail.