Speakers of English around London and some other parts of the UK are often criticized for th-fronting, or pronouncing "th" as /f/ or /v/. But you know who else did this? The ancient Romans.
(Okay, it's not technically the Romans, but their ancestors. I'll get to that in a minute.)
Latin is part of a subfamily called Italic, which includes a bunch of dead languages like Oscan and Umbrian that Latin killed off as it expanded.
Proto-Indo-European, the ancestor of Italic, Germanic, Celtic, and more, had a series of voiced aspirated stops—that is, sounds like /b/, /d/, and /g/ that were followed with a puff of air.
In the Germanic subfamily (which includes English), the aspiration went away, leaving a plain /b/, /d/, or /g/ as in "boy" or "dog" or "girl". But something different happened in Italic.
At the beginning of a word, those aspirated stops turned into fricatives. (A fricative is a sound like /s/ or /f/ that's made by forcing turbulent air through a small opening.)
So /bʰ/ (with the superscript ʰ indicating aspiration) became /f/, and /gʰ/ became /x/ (the final consonant in "loch") and then /h/.
The sound /dʰ/ became /θ/ (the initial consonant in "thin"). And then, just as is happening in the UK, that "th" sound became /f/.
The upshot of this is that a lot of Latin words beginning with /f/ correspond to Germanic words beginning with /d/.
So the Latin word for 'make, do', "facere", is cognate with the English "do". "Forum", meaning a place enclosed by doors, is cognate with the English "door".
Maybe in a few centuries "th" will regularly be pronounced /f/ in English. After all, it's kind of an unusual sound across languages.
At that point, it will just be the normal way to pronounce those letters (assuming there's been no spelling reform) and not some kind of stigmatized form.
But I have to wonder if ancient Italic speakers ever groused about Kids These Days saying "thacere" as "facere".
