Please tell me which four releases you are talking about. I'm the MemShrink project lead. It's a common misconception that we claim memory improvements all the time, but it's just not true and it drives me crazy.
If you look at the release notes, we claimed improvements in add-on memory consumption for Firefox 15, and general improvements for the browser itself in Firefox 7. (And also Firefox 3, I think, but that's ages ago predates my time working on the project.)
I really want to understand where this misconception comes from. I think repeated reporting in the tech press of the same improvement as it moves from Nightly to Aurora to Beta to release might be the cause.
If you look at the release notes, we claimed improvements in add-on memory consumption for Firefox 15, and general improvements for the browser itself in Firefox 7. (And also Firefox 3, I think, but that's ages ago predates my time working on the project.)
I know this because I wrote the accompanying blog posts for those two releases (https://blog.mozilla.org/nnethercote/2012/07/19/firefox-15-p... and https://blog.mozilla.org/nnethercote/2011/08/09/firefox-7-is...) and liaised with marketing about the release notes.
I really want to understand where this misconception comes from. I think repeated reporting in the tech press of the same improvement as it moves from Nightly to Aurora to Beta to release might be the cause.