I've seen similar issues simply by using Linux as my main desktop... some sites just won't work because of it, or seem to filter out "Linux" in the user agent. Which kinda sucks.
This is one of the reasons why all of my browsers identify as a recent Chrome version. All of those problems just up and disappear. I started doing that when Google claimed (lied) that some of their products no longer support Firefox and would block me from accessing right up until my browser identified itself as Chrome. No bugs, no issues.
If market competition law wasn't reduced to dead ink, lying about your competitor's product, or abusing your dominance in one market to dominate another market, would at minimum carry painful fines.
I agree that lying should be illegal, but “domination” is vague. One could argue (and I would agree) that there’s nothing wrong with dominance if it comes down to just offering a superior product.
And why should the cross-market context be treated differently?
Web services could have at least one developer using Firefox and another one using Safari. I'm the one with Firefox for my customers. Their web apps work with at least Chrome and Firefox. Safari is on them, if they have a Mac. Nobody ever complained.
This is the exact same situation that got Microsoft tied up in endless antitrust investigations 30 years ago. Of course that was back when the US still had a government rather than a service bureau for billionaires.
And why should the cross-market context be treated differently?