Animations are not important enough to justify. Not wanting to serve all your content from a single domain is not enough to justify. These are excuses, not technical reasons.
They're short cuts you might take to get a product out and get early feedback, the same sort of shortcuts most of us have taken when pushed to release something sooner. This is a product in Beta, not the finish article.
Even if everything work in theory just dropping multi-browser testing would save time. If their aim is a beta product for early user testing, I really don't think what they've done is unreasonable.
Getting a product out in the web development world includes getting it out for other browsers than the browser you develop in house. Otherwise, you won't get the early feedback you wanted. Especially when your application is working, with some minor glitches.
It's not like the application is completely broken in Firefox with the fixes mentioned. Bypassing CSP for your own domains feels like a hack that you shouldn't be able to do.
Given how over subscribed the beta is I think they're getting feedback.
Remember with this sort of product the questions they have are "is this interesting?", "is this useful?", "do people like what this does?".
Can we get this running on Firefox simply isn't an interesting question to them - they know the answer, it's yes if they throw resource at it, but for a new product team with questions over whether this product should even exist that's not a priority.
Remember, this is Google who have a long history of canning this sort of project. If I were the company who produced Wave, I'd probably look at how I could reduce the cost and time to feedback for my next new thing too.
As an aside, I've tried Inbox and, to me at least, it's the next Wave, not the next Gmail.
You have to admit it seems a little shady when it comes from the browser vendor. It would be fine if the message said, "we haven't tested this, it might not work, YMMV". Instead, the message says, "click here to download our product", the implication being they'd like you to convert to only ever using their product.
I might agree with some things but not with e-mail, it's too important to most people say "hey this is probably OK but who knows".
And because of that there is the risk of reputational damage around one of their core products. Working in tech you understand what a Beta really means and you can make that call on an informed basis but that's not true of a typical G-mail user today.
It doesn't sound like they're dropping e-mails or anything else painful like that (something I've experienced several times trying to run GMail on Firefox and/or Opera). It sounds like they wanted to break CSP and have some animations and not have to worry about proper data modelling. Or maybe they just want to keep throwing rocks at people using browsers other than their own.
They're short cuts you might take to get a product out and get early feedback, the same sort of shortcuts most of us have taken when pushed to release something sooner. This is a product in Beta, not the finish article.
Even if everything work in theory just dropping multi-browser testing would save time. If their aim is a beta product for early user testing, I really don't think what they've done is unreasonable.