Can I make Firefox the default browser in iOS [duplicate]

You cannot change the default browser (Safari) unless you jailbreak, which you do not want to do. You can however use supported apps. For example, just like how ads in browsers may open app store "sponsored" apps, YouTube will open Chrome if enabled to. If the app does not specify which browser to launch in when a browser-required link is clicked, Safari will be launched.

If programmed to do so, apps are well able to launch (and transmit data) to other apps. You cannot change Apple's iOS default settings but you can decide which apps you use such that the apps you like will be supported.

Update (2019) : The "Share" option in iOS may be able to launch specific browsers, eg: Firefox has this option.

I have been using Firefox since it was a new experimental program called Phoenix. I downloaded the Gecko rendering engine to play with when it still fit on a single 1.44 mb floppy. It's my only real browser, and one of the first things I install on a new system. I don't use Mail.app or Safari.

Except on iOS. The only thing I value on iOS is stability. I live with the default mail and browser clients because they work, there are no required workarounds, and no added overhead. Every "alternate browser" on iOS is Safari with a different skin and no access to the faster JavaScript engine. Yes, I lose Firefox Sync on my iPhone and iPad. But it works.

If you want an all-Firefox ecosystem, you will either have to live with the inherent problems on iOS or give up on that one battlefront. There is a reason that Mozilla didn't release Firefox for iOS for so long - they were hoping Apple would back down and allow some freedom. Apple didn't. Mozilla has to live with it. Chrome on iOS has the same restrictions. No add-ons, no ability to make it the universal default browser.

Use Apps That Work Together

Apps can launch other applications, so you can take advantage of this to build ecosystems of apps that work well together and use each other as the defaults.

Google’s iOS apps are the star of the show here. Let’s say you have Chrome, Gmail, and Google Maps installed. When you tap a link in the Gmail app, it will open in the Chrome app. When you tap a map link in Chrome, it will open in the Google Maps app. And, when you tap a business’s email address in the Google Maps app, it will open in the Gmail app.

If you want to change default apps because you really prefer Google’s services, try just using as many of Google’s apps as possible. They’ll work together and allow you to avoid the standard iOS apps as much as possible. If you use third-party apps, hopefully they offer support for choosing your own preferred apps.

In case of Firefox I haven't heard or done anything of this sort.