Ehh
There's a clear difference between accepting money from an entity and letting it control things and make decisions. Pushing for a full and clear separation from any potential conflict of interest (while noble) is how projects die.
I'd love for Firefox to be fully funded through small anonymous public donations in an ideal world. As it is, I don't see an issue from taking Google's money to do something that most users would want anyways.
If the default search wasn't google, I'm certain even more users would bail on Firefox. Anyone who does want an alternative search engine is capable of clicking on it during installation.