Certainly you are tracked if you use the default Google search, but even if you change to another search ther are remaining the Google APIs in FF, which you can desactivate in Vivaldi, but not in FF

I think you have read more than only the first lines of the links

Fact: In addition to the Google cash flowing to Mozilla, a number of Google engineers spend significant amounts of time working on Firefox. This includes Ben Goodger, the former lead developer, and still a major contributor for the browser. Yes, other companies pay developers to work on Firefox, but none throw as many overall corporate resources at the browser.

Fact: Two key features of the Google Toolbar for Firefox were rolled into the Firefox 2.0 browser and are turned on by default: Google Browse By Name and Google Safe Browsing for Firefox (now the Phishing Protection feature in Firefox 2.0). These two features, while useful, are more than just the application of a useful patch. They result in millions of Firefox browsers regularly polling Google servers for core information.

Fact: The Google Anti-Phishing relationship will be expanded in Firefox 3.0. While Google currently is the default provider of a blacklist of known phishing sites to the browser, this will be enhanced to include a blacklist of sites that serve up malicious software.

Mozilla and FF are great in the past and FF is a good browser, but currently is a Google pet. Things which happens dealing with the devil, loosing independence. BS if you believe any other thing.