I have a little personal webapp I use on my iPhone, that relied on Bootstrap3 glyphicons. However on my iPhone it started displaying weird emojis instead of the icons after upgrading to iOS 11. Other people's iPhones displayed everything fine, desktop browsers displayed everything fine, seemed to be just my phone, WTF?
Even looking at the BS3 components sample page I'd see emojis, WTF!?
Tried switching to open-iconic fonts, same problem (different emojis though), WTF!!?
Finally found this coment on BS3's Github saying it was due to content-blocking. Turns out I had Firefox Focus installed, and probably during the iOS upgrade I also upgraded Focus which must of coincidentally starting blocking the webfonts at that time.
Disabling content-blocking fixed the problem, yay! Just as a reference, the place to go (at least in iOS 11) is:
Settings App, scroll down to "Safari", scroll down to "Content Blockers", then in "Allow These Content Blockers:" disable "Firefox Focus"
Mozilla's Focus support page says:
Web fonts - fonts that are downloaded from the server (may slow down web pages). Web fonts are typefaces used to style the text on some web pages. Blocking Web fonts will alter the appearance of text on any pages where Web fonts are used, but all text will still display legibly.
Someone should tell them web fonts are used for more then just text, and blocking them can make your icons illegible.
Fortunately, you don't have to completely give up Focus content-blocking. In the Focus app, there's a little gear icon in the upper-right that lets you in a more fine-grained fashion enable/disable blocking of web fonts, but keep the other blocking of ad trackers, etc. After turning only web-font blocking off, and re-enabling content-blocking overall in the phone's Safari settings, I still have working icons in my little app.