More specifically, The relationship Google has with government agencies and how they spy, on everyone.
I've been specifically referring to Chrome/Chromium as something separate from any Google (online) services for a reason. You have control over the software that you have installed and if you really wanted to you could start capturing packets to look for signs of "phoning home" (which you won't find).
I'm not trying to say that there isn't a relationship between the company and the government. I'm trying to say that on the software side of things the benefits outweigh the risks (where there is very little likelihood of there being any) because you have a certain amount of control over it. With Chromium you even have the src.
Just like when the NSA asked Linus Torvalds to create backdoors in Linux for them, but of course US companies would have caved to the pressure.
I seriously doubt the NSA needs backdoors inserted into the Linux kernel considering the sad state of security and lack of caring about it in the vanilla kernel. This also applies to linux in general but there has been a push in recent years to improve upon this on the software side of things (see: Debian using hardened binaries for certain services). One good thing about using Firefox on Ubuntu is I believe they ship with Appamor profile's (MAC) by default (I'm not sure about Debian). They may not be the most restrictive but it's an improvement nonetheless (and probably makes things better than on the Windows side of things with Firefox).
I like Debian, I like their package management, I have Debian on my server. I think the possibilities to secure a Linux environment are better than on Windows which is why I like it on servers. You can create a very restrictive policy with grsecurity's full system learning mode with minimal effort which is good because people will use stuff if there isn't a lot of effort involved or there isn't a large barrier to entry (this is extremely important). A counterexample to this is UAC in Vista pre-SP1 (IIRC) which was really annoying and everyone just wound up disabling it despite the benefits of having UAC enabled (you should have it enabled always).
This post may have been slightly off topic but I still think it relates to the never ending cycle of software bugs, some of which have been around for a while, and measure that can be taken to protect yourself.