Signup fails silently in Opera

I received an invitation and when trying to sign up in Opera, the button just keeps spinning after entering all information.
The following stack trace is printed in the console:

```
Uncaught exception: Error: No rng found; tried requiring "crypto" and window.crypto
Error thrown at line 35, column 56237 in (e) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
throw new Error('No rng found; tried requiring "crypto" and window.crypto');
called from line 35, column 57899 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
i.push(e.now_to_buffer()),i.push(new t(c)),i.push(h(u)),i.push(e.now_to_buffer()),s=t.concat(i),a=o.from_buffer(s),_.scrub_buffer(s),f=0,l=i.length
called from line 21, column 53478 in (e) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return this.continuation?(t.__active_trace=e,n=this.continuation,this.continuation=,n(this.ret)):t._warn("Entered dead await at "+t._trace_to_string(e))
called from line 21, column 54013 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return e._call(t)
called from line 21, column 53014 in (n) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return t.tickCounter(500)?"undefined"!=typeof e&&null!==e?e.nextTick(n):setTimeout(n):n()
called from line 21, column 53868 in (e, t) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return--this.count>0?void 0:i.trampoline(function(e){return function(){return e._call(t)}}(this))
called from line 21, column 51871 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return o=1<=arguments.length?r.call(arguments,0):[],null!=n&&null!=(a=n.assign_fn)&&a.apply(null,o),e?(s=e,u||(e=null),s._fulfill(i,f)):t._warn("overused deferral at "+t._trace_to_string(f))
called from line 37, column 18799 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return t(s)
called from line 37, column 17985 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return t(o)
called from line 37, column 17934 in (t) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return l=function(){return t(o)},p=function(){return r.trampoline(function(){return c(t)})},h=function(e){return o.push(e),p()},e>i?void!function(e){return f.entropies.length?(n=f.entropies.splice(0,1)[0],i+=n[1],e(s.push(n[0]))):void!function(e){a=new r.Deferrals(e,{parent:u,filename:"src/generator.iced",funcname:"Generator.generate"}),setTimeout(a.defer({lineno:22}),f.loop_delay),a._fulfill()}(e)}(h):l()

Error created at line 35, column 56237 in (e) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
throw new Error('No rng found; tried requiring "crypto" and window.crypto');
called from line 35, column 57899 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
i.push(e.now_to_buffer()),i.push(new t(c)),i.push(h(u)),i.push(e.now_to_buffer()),s=t.concat(i),a=o.from_buffer(s),_.scrub_buffer(s),f=0,l=i.length
called from line 21, column 53478 in (e) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return this.continuation?(t.__active_trace=e,n=this.continuation,this.continuation=null,n(this.ret)):t._warn("Entered dead await at "+t._trace_to_string(e))
called from line 21, column 54013 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return e._call(t)
called from line 21, column 53014 in (n) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return t.tickCounter(500)?"undefined"!=typeof e&&null!==e?e.nextTick(n):setTimeout(n):n()
called from line 21, column 53868 in (e, t) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return--this.count>0?void 0:i.trampoline(function(e){return function(){return e._call(t)}}(this))
called from line 21, column 51871 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return o=1<=arguments.length?r.call(arguments,0):[],null!=n&&null!=(a=n.assign_fn)&&a.apply(null,o),e?(s=e,u||(e=null),s._fulfill(i,f)):t._warn("overused deferral at "+t._trace_to_string(f))
called from line 37, column 18799 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return t(s)
called from line 37, column 17985 in () in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return t(o)
called from line 37, column 17934 in (t) in https://keybase.io/_/brew/_/ab1a6f18/sitewide-js.js:
return l=function(){return t(o)},p=function(){return r.trampoline(function(){return c(t)})},h=function(e){return o.push(e),p()},e>i?void!function(e){return f.entropies.length?(n=f.entropies.splice(0,1)[0],i+=n[1],e(s.push(n[0]))):void!function(e){a=new r.Deferrals(e,{parent:u,filename:"src/generator.iced",funcname:"Generator.generate"}),setTimeout(a.defer({lineno:22}),f.loop_delay),a._fulfill()}(e)}(h):l() Timeout thread: delay 10 ms eb2a8b71c5499d888638ac0d:35
```

Reproduce the signup flow in Opera and inspect the stack trace around sitewide-js.js, especially the reported “No rng found” error. Determine why signup cannot obtain randomness in that browser; done means an invited user can complete signup without the button spinning indefinitely.

Written by the indexing model from the issue text.