This is not a comprehensive encyclopedia, but these are patterns we have met in the past for identifying user agent strings which are broken or future

Encyclopedia Of Broken UserAgent String Detections

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2022-01-25 07:00:05

This is not a comprehensive encyclopedia, but these are patterns we have met in the past for identifying user agent strings which are broken or future fail.

This is a fairly common mistake, most of the detection algorithm have been fixed when browsers switched their versions from one digit to two digits, but there is still code out there relying on fixed lengths.

Many sites have a grid for the minimum version number supported for each browsers. The current Firefox User Agent string on iOS has this pattern.

Mozilla/5.0 (iPhone; CPU OS 14_4_2 like Mac OS X) AppleWebKit/605.1.15 (KHTML, like Gecko) FxiOS/33.0 Mobile/15E148 Safari/605.1.15

Notice that FxiOS/33.0 means Firefox on iOS version 33. Web developers often used a up to date library that will return something like:

So far so good. The issue starts when the site says: "Oh. It's Firefox on Mobile, so it means this is Android. We support Firefox on Android starting Firefox/78". Then they block the access to the full site, or the video, or asking the user to upgrade their browsers while they are on the latest version of Firefox iOS.