We keep making incremental improvements with every minor release and why we have been doing them weekly.
Were going to publish an assessment of v15 and v16 (including minors) to show the improvements.
When you install a new version of SmarterMail, new files will be downloaded. After that, they are cached. There was an issue on the original 16.x release that had an issue with caching.
We are still trying to figure out what is causing Firefox to be slow. Were showing no CPU and were seeing no Bandwidth being used but Firefox just sits there dumbfounded. Its random and difficult to diagnose.
Hope this helps,