FeedBurner proxy wizard fails to advance with ampersands in feed URL
FeedBurner's "Create proxy" wizard silently refuses to advance past step 1 when the source feed URL contains an ampersand.
Paste a multi-param feed URL, e.g. https://old.reddit.com/r/Bogleheads/top/.rss?t=day&limit=25, and click Next. Nothing happens. The wizard stays on step 1 with no validation error, no toast, nothing red. It looks exactly like the click never registered, so you waste time on your automation/input layer instead of the URL.
The click does register. The form POSTs to https://feedburner.google.com/_/prefillproxyparams with body ["<your url>"], gets HTTP 200 back, and the payload carries a null result in slot 1:
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[["prefillproxyparams:xhr",null,16],["di",466],["af.httprm",466,"...",33]]How do you burn a feed whose upstream URL needs two query parameters?
A single query parameter is accepted; two joined by & are not. Presumably the un-decoded & truncates the URL server-side.
Drop to one param and the same endpoint returns the feed title plus a suggested slug, and the wizard advances:
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[["prefillproxyparams:xhr",["top scoring links : Bogleheads","/reddit/Wl8u1RSWciS"]],...]Measured 2026-08-21, burning reddit RSS feeds:
.../top/.rss?t=day&limit=25 | null prefill, stuck on step 1 |
.../top/.rss?t=day | advances, title prefilled |
.../new/.rss?limit=100 | advances, and limit=100 IS honored (FeedBurner serves 100 entries) |
.../top/.rss (bare) | advances |
Fix: fold the second parameter into an upstream default. For reddit RSS, limit already defaults to 25, so ?t=day is semantically identical to ?t=day&limit=25 — confirmed by fetching both variants directly from reddit and comparing t3_ entry id sets (identical). If you truly need two non-default params, FeedBurner cannot express it; use a different intermediary.
Diagnostic that saves the most time: ignore the UI and watch the prefillproxyparams response. null in slot 1 means rejected, [title, slug] means accepted. The UI shows you neither.
Unrelated but adjacent, since people hit it in the same session: FeedBurner does honor a single ?limit=N, and it re-serves the upstream Atom essentially untouched — no feedburner namespace, no feedproxy.google.com link wrapping, and the upstream <title> survives rather than being replaced by the proxy title you typed.