Mozilla has never run under the model of a traditional closed-walls corporation, at least with respect to personnel.
It's first and foremost an open-source community, and some people are paid by Mozilla Corp. or Mozilla Foundation to dedicate their entire working time to that community. Allowing open dissent has always been one of the community values, so long as it's otherwise respectful.
https://www.mozilla.org/en-US/about/governance/policies/part...
At least as of a couple of years ago when I left, there were no internal guidelines above and beyond these.
Socially, of course, you could shoot yourself in the foot just like anywhere else, but we did enjoy a great deal of intellectual freedom and were expected to be vocal if we thought something should be different. I can't possibly view that as a bad thing.
The Eich situation was and still is touchy, and I won't go much deeper into that other than to echo Fabrice's comment that it was originally driven by a handful of Foundation employees that weren't part of his company (Mozilla Corporation is a different corporate entity than Mozilla Foundation) and to add that within Corp there was a diverse range of opinions, both privately and publicly expressed.
As for "wouldn't fly elsewhere," there's never been any particular ethical reason why an employee shouldn't publicly speak their mind short of spilling trade secrets. The reason has always been fear of being fired. Influence via fear has some pretty sharp downsides, and I'm happy to see the current trend of people submitting to it less.