Several comments point out this doesn't happen on Android.

I'm using Android, with my default browser set to Firefox Focus, and I found:

- Every few months, the default browser gets reset to Chrome. I don't know this has happened until I realise I'm looking at something in Chrome. Then I look at the default browser setting, see it changed to Chrome (without my consent, and as far as I know, no notification), and I change it back to Firefox Focus. This has happened at least twice in the last year.

- For a while, when opening things from Google Search it opened them in Chrome. However I'm unable to replicate that now.