It was bound to happen sooner or later -- today Google officially turned it's nose on Firefox by removing it's default status in "Google Pack". Instead of that popular open source browser, Google is now recommending Chrome to users that have Google Pack instead.
This is the third blow that they have has delivered to Mozilla -- the one last strike would leave the company in a very difficult position.
The first blow to Mozilla was the actual launch of Google Chrome -- the browser was touted as being faster and more secure than the other popular browsers, and got a lot of press out of the gate. The browser was received well, except for the initial EULA hiccup soon after release.
Second, Google removed any sort of promotion for Firefox on Google properties -- including ads that were once found on the main page. Instead, Google has been advertising their new browser on some of their most popular properties.
The removal of Firefox (replaced with Chrome) is their third attack on Mozilla -- it's unclear how many people use Google Pack, but you can be sure most novice users who do won't be installing Firefox. Mozilla must be starting to wonder how aggressive Google is going to get with their new browser.
The last (and final, I think) move that Google could make would be to remove themselves as Mozilla's main source of income. About $60 million per year (that's around 85% of Mozilla's total income) comes from Google to ensure they remain the default search engine on the browser. Canceling this relationship could seriously damage Mozilla, unless a company like Microsoft decides to start giving their largest browser competitor the cash it needs to survive -- an unlikely, but possible scenario.