Comparative advertising is legal in some (most?) European countries -- it's definitely legal where I'm from (and AFAIK it's also been legal in Germany for a while, although it has been banned for a long time). However, in most cases, if you want to do it, you have to do it based on clear metrics that your audience can verify.
So for example it's legal to show an ad saying that Edge is faster than its competitors, but you have to write a small note somewhere that says who measured that and how.
(Technically I think you can even call the competitors by name, but virtually no one does it because the public doesn't really appreciate that. Most companies will, at most, give a subtle hint).
It is, however, illegal to show an ad which simply says or implies that Firefox is somehow worse than Edge, or that no one uses it anymore, or that it's old, or whatever, without explaining how you got to that conclusion. It's fine to say that Edge is the most popular browser and link to a page about the study that showed it (or the study itself). But without the numbers, you're not allowed to do it. The studies in question are rarely truly objective, but they do offer useful data points.
That's intended to ensure that a company which is perceived as reliable or trustworthy cannot abuse that position and engage in false advertising.
This is a pretty good example -- among non-technical users, who make up the vast majority of computer users in the world, Microsoft is perceived as a solid and reliable company (and, the whole ads and data collection thing aside, it's perceived that way among technical users, too, yours truly included). Their word carries some weight, and non-technical users are likely to take their word at face value.