I somehow agree with this "if your client-side MVC framework does not support server-side rendering, that is a bug. It cripples performance." and it always felt right.
I would straight forward look for skillsets and productivity(productivity includes guys availability i.e. whatever is needed) and attitude rather than age, Period.
My intention was not to sound like rant but if I did then it's my bad. I notice the issues with ubuntu a lot and I was big fan of it as mentioned above but not anymore as you know the reason. I get paid for developing application which work on browsers and not make browsers work fast. The point is big number of devs won't be able to give their time to make browsers better but that does not mean they can't say bad is bad.
I'm sorry, but Chrome doesn't work better then Firefox on Ubuntu. Actually, you need to install Chromium instead! You pointed Chrome + Ubuntu, which is not very stable compared with Chromium.
For web development, I think the Dev tools on FF are getting better, so I'm still using Firebug. I often use both Firefox + Chrome and I don't think one is better then another. I do trust Firefox, comparing with Chrome, the latest looks like a bot, maybe google new web spider ? Well, looks like (Urls magically appearing in their list, etc), not sure.
Firefox and Chrome teams are extremely important, they're bringing new stuff all the time, researching, etc! I wouldn't say their work is bad!
I don't have problems even with 25 version but again that might be very individual: different sites, different projects and etc.
There is one little thing you can do: enable all reporting in Advanced settings if you have not done that yet. Mozilla will get at least some information that might be later used for browser improvements.
The difference in speed between Python and PHP should not be a deciding factor in choosing between the two web frameworks. Many of the core PHP functions are implemented in C directly, so they are very fast, but once you add a framework into the mix, speed drops off considerably because it seems the PHP interpreter is not so good.