Stale/broken `from-browser` URLs triggers an error message that starts with "Error: Error: "

[dholbert]

STR:

1. Visit https://profiler.firefox.com/from-browser/calltree/
   (or, capture a profile, and don't upload it, and then quit and session-restore Firefox, including that tab. This results in a URL like that^ with a long suffix)
2. Look at the error message shown in the page and in the web console.

ACTUAL RESULTS:
Both the page and the Web Console show:

Error: Error: Could not find a profile for this tab.

EXPECTED RESULTS:
No double-"Error" prefix.

If it's helpful, here's full message from Web Console, including the error message and the backtrace. Note that the error is attributed to something in web-channel.ts, called into from receive-profile.ts.

Error: Error: Could not find a profile for this tab.
    a web-channel.ts:248
    AT receive-profile.ts:1061
    Redux 2
    MR receive-profile.ts:1398
    Redux 2
    _processInitialUrls UrlManager.tsx:123
    componentDidMount UrlManager.tsx:208
    React 44
    Kk scheduler.production.js:151
    (Async: EventHandlerNonNull)
    lz scheduler.production.js:200
    n chunk-FFESA2B5.js:1
    cz index.js:4
    n chunk-FFESA2B5.js:1
    NU React
    n chunk-FFESA2B5.js:1
    RU React
    n chunk-FFESA2B5.js:1
    <anonymous> index.tsx:18

┆Issue is synchronized with this Jira Task