This is the most relevant of your 3 examples and Canonical got heavily criticised for it. They ended up reversing their decision. Which makes it all the more important that people take this example not as "It's ok for Microsoft to do it as well" but rather "We also shouldn't allow Microsoft to get away with this".

>Firefox was paid by Google In the last and I believe Yahoo these days.

The thing here is that when you type something in the search bar you are actually wanting to search for something online - given that it's a "search" bar. It kind of made sense for Google to be the default search engine as that is the most popular search engine in the west (ie what most people would prefer to default to) so even without Google's investment I can see the logic of having a Google search bar. In fact I would go further and say that's a well received productivity tool.

However It's also very easy to change which online service is used in the search bar - or even to remove it entirely. So the Google investment does not lock you into using Google services on Firefox.

Thus I see no conflict of interest with regards to Google's donations to Firefox.