Firebase Auth → PostHog · Conversion tracking
Connecting Firebase Authentication to PostHog
Firebase Auth is usually the identity layer in a mobile-first product, which means the user ID it issues is the only thing connecting a web visit to an in-app purchase. PostHog can be self-hosted, which changes the calculus entirely: the data stays on infrastructure you control, and so does the responsibility for everything that goes wrong with it. The join between them succeeds or fails on one thing: whether the distinct_id reaches the Firebase user identity before the conversion happens, because PostHog can only match a conversion it can tie back to a click it recognizes.
✓ 30-minute call · No commitment · You leave with a written remediation plan even if we’re not the right fit.
Written guarantee
95%+ conversion accuracy on Firebase Auth → PostHog
Measured against your own order records at handover. Miss it and we keep working at no cost until it’s met.
Built on — and certified for — the platforms that matter
Stape
Pro Partner
Meta
Tech Provider
Tag Manager
TikTok
Events API
Microsoft
UET Partner
CAPI Partner
CAPI Partner
Built on the same partner stack used by enterprise DTC brands.
By the numbers
No fake testimonials.Just the math.
70+
Platforms supported
Shopify · Woo · Magento · BigCommerce · 65 more
8+ / 10
Meta EMQ guaranteed
in writing — keep working free until hit
2–4d
Build to live
accurate data flowing within 7 days
$0
Monthly fees, ever
one-time fixed price · you own the stack
400d
Cookie lifetime
max RFC 6265bis allows · 57× Safari ITP
9
Ad channels covered
Meta · Google · TikTok · MS · LI · Pin · Snap · Reddit · X
95%+
Tracking accuracy
verified vs Stripe · GA4 · ad-platform reports
30 min
Free founder call
no SDR · no pitch deck · written remediation plan
Every figure above is either a commitment we put in writing or a countable fact. What your own setup is losing is not on this list, because we haven’t measured it yet — that happens on the call, against your own order records.
Real clients · real videos · real outcomes
Don’t take our word for it. Watch the receipts.
Founders, marketers, and agency owners describing the before-and-after of their Firebase Auth → PostHog tracking rebuild — in their own words, on camera.
Why this join usually fails
The distinct_id never reaches Firebase Auth
The single most common cause. Anonymous authentication creates users before signup, and linking an anonymous account to a real one is a step teams frequently skip.
Anonymous accounts never linked to real ones
Firebase's anonymous auth is convenient and creates a separate user. If it is not linked at signup, the pre-signup activity and the paying customer are two different people in every downstream system.
Self-hosting the analytics and the outage together
The advantage of owning the pipeline is that nothing blocks it. The cost is that when the ingestion instance fills its disk on a Saturday, the events are gone and nobody is paged. Hosted tools fail differently and more visibly.
Nothing reconciles afterwards
An upload that succeeds is not an upload that matched. PostHog shows events in the activity view within moments. On a self-hosted instance, check the ingestion lag as well — events that are queued are not events that are lost, and the two need different responses.
Architecture
How Firebase Auth and PostHog actually connect
Two systems that know nothing about each other. Everything below exists to give them one shared reference.
Step 1
Firebase Authentication holds the truth
Firebase holds identity, not revenue. Its value to measurement is that it gives a stable key that survives the web-to-app transition where every cookie dies.
Step 2
PostHog needs a click to match
PostHog needs a distinct_id, an event name and its properties. Self-hosted instances additionally need the ingestion endpoint reachable and the project API key correct, which is a class of failure hosted tools do not have.
Step 3
The identifier is the bridge
The distinct_id, captured at the visit and carried into the Firebase user identity. Without it there is nothing to join on and no tool fixes that.
Step 4
The event source decides reliability
Send paid conversions keyed on the user identity. Signups and anonymous sessions are stages, not revenue.
Step 5
Deduplication at the destination
PostHog deduplicates on the event UUID where supplied. Without one, a retried batch duplicates, and on a self-hosted instance there is no vendor support desk to notice it for you.
Diagnose it honestly
Working vs. broken, side by side
Both states look identical from the PostHog dashboard, which is why this runs for months before anyone notices.
Normal — not a fault
The distinct_id present on the account
Visible on the record itself in Firebase Authentication, not merely captured somewhere on the site.
Sent from your billing system, keyed on the user ID
Server-side, so it does not depend on the customer's browser still being there.
Deduplicated correctly
PostHog deduplicates on the event UUID where supplied. Without one, a retried batch duplicates, and on a self-hosted instance there is no vendor support desk to notice it for you.
Reconciles with the source
PostHog's count and Firebase Authentication's records agree within a few percent over a closed window.
Actually broken
The distinct_id missing on most records
Anonymous authentication creates users before signup, and linking an anonymous account to a real one is a step teams frequently skip.
Sent from the browser
Anyone who closes the tab, blocks the script or converts without a page load is invisible. Firebase's anonymous auth is convenient and creates a separate user. If it is not linked at signup, the pre-signup activity and the paying customer are two different people in every downstream system.
Counted twice, or not at all
The advantage of owning the pipeline is that nothing blocks it. The cost is that when the ingestion instance fills its disk on a Saturday, the events are gone and nobody is paged. Hosted tools fail differently and more visibly.
Nobody has reconciled it
The dashboard shows a number and no one has compared it to Firebase Authentication. A wrong number that nobody checks is indistinguishable from a right one.
Diagnostic sequence
Diagnostic order
Each step rules out a class of cause. Run them in order and the last one usually has a single explanation standing.
- 1
Count accounts carrying the distinct_id
The ceiling on everything else. Do this before debugging anything downstream.
- 2
Follow one real conversion end to end
From the ad click through Firebase Auth and into PostHog.
- 3
Check whether anonymous accounts are linked or orphaned at signup
Orphaned anonymous users are the most common Firebase identity failure and they silently break every cross-signup funnel.
- 4
Check ingestion health and disk before debugging any missing event
On self-hosted instances the answer is infrastructure far more often than it is instrumentation.
- 5
Read the match rate, not the success message
PostHog shows events in the activity view within moments. On a self-hosted instance, check the ingestion lag as well — events that are queued are not events that are lost, and the two need different responses.
Source-of-truth validation
How it gets proven
Against Firebase Authentication's own records, not against either platform's dashboard.
- The distinct_id confirmed present on a live account.
- A real conversion followed from click through Firebase Auth to PostHog.
- Purchase events reconciled per transaction against your billing system, with ingestion lag checked over the same window.
- Paid conversions reconciled per linked user identity against imported conversions.
- Reconciled over a fully closed window, matched per record rather than on totals.
- Re-checked 30 days later.
Straight talk
When you don't need this
Worth reading before paying anyone, including us.
- If PostHog already reports conversions that reconcile against Firebase Authentication's records within a few percent, this join is working and there is nothing to buy.
- Measure identifier coverage yourself first — pull your last hundred accounts and count how many carry the distinct_id. Ten minutes, free, and it tells you whether any of this is worth doing.
- If you do not use anonymous auth, the linking problem does not arise.
- If you have no reason to keep the data on your own infrastructure and no team to run it, the hosted product removes the only real downside of this one.
Who this is for
Honest about who we’re a fit for.
We don’t take every project. Here’s how to tell if we’re right for you.
You’re a great fit if…
- You run Firebase Auth → PostHog (or are migrating to it)
- You spend $5K+/month on paid ads (Meta, Google, TikTok, Microsoft, LinkedIn)
- Your reported ROAS doesn’t match what your bank account is saying
- You want to own your tracking stack — no monthly SaaS fees forever
- You have 2–4 days to do this once and never think about it again
Skip us if…
- You spend less than $500/month on paid ads (browser pixel is fine)
- You want a SaaS dashboard with monthly fees forever (Triple Whale, Hyros)
- You need attribution modeling — we fix the data foundation, not multi-touch reports
- You want a 6-month enterprise consulting engagement (we ship in 4 days)
- You expect us to manage your ad accounts (we don’t — that’s a different service)
If you’re still unsure,book the call anyway— we’ll tell you straight whether we can help.
What working looks like
The distinct_id on every account
Server-sideCaptured before the conversion and stored where it survives.
Conversions arriving in PostHog
8+ EMQThe event lands on the person profile and becomes available in insights, funnels and session replay.
Reconciled against the source
DedupedFirebase Authentication's own records are the reference, not either dashboard.
What gets built
Identifier capture into Firebase Auth
Capture the identifier on the web, write it to custom claims or your own user document at first auth, and link anonymous accounts rather than creating duplicates.
Event source: your billing system, keyed on the user ID
Send paid conversions keyed on the user identity. Signups and anonymous sessions are stages, not revenue.
Dispatch to PostHog
The PostHog capture API, posted server-side from your backend to your own instance or to PostHog Cloud.
Reversals where they exist
Cancellations reverse against the same identity.
Pick the package that fits your ad spend
Fixed-fee, no surprises. If your ad spend is meaningful,server-side tracking is what we recommend— it’s the only setup that survives iOS, Safari ITP and ad blockers.
Browser-side starter
Wires the join and verifies it on a live conversion. Honest about its ceiling where the source can only be read from the browser.
- The join built and tested end to end
- Verified on a real conversion
- Reconciled against the source's own records
- Written handover
1st-party server-side
Save $18K–$120K over 5 years vs Triple Whale / Hyros
The join built server-side from the source's own records, so it does not depend on a browser being present when the conversion happens.
- Events sourced from the system of record, not the browser
- Identifier captured and persisted end to end
- Deduplicated at the destination
- Reversals wired where the source supports them
- 95%+ accuracy guaranteed in writing
Full 1st-party stack
Every destination fed from one place, plus monitoring so a broken join surfaces in days rather than at quarter end.
- Everything in 1st-party server-side
- All paid destinations from one container
- CRM and offline loop
- Refunds and cancellations reversed everywhere
- Monitoring per destination
Not sure which tier fits?Book a 30-min scoping call— we’ll tell you straight, no upsell pressure.
How it works
Built in 2–4 days. Accurate data within 7.
We deliver the entire 1st-party server-side stack in 2–4 business days. You start collecting accurate, deduped conversion data the moment it goes live — and within 7 days every signal is flowing cleanly to Meta, Google, TikTok and the rest.
Kickoff + audit
30-min call. We map your current pixels, GTM, dataLayer, consent setup, and ad-platform integrations. You get a written report of every leak.
Build the stack
Server-side GTM container deployed on your subdomain. Meta CAPI · Google EC · TikTok Events API · Microsoft UET wired. Identity match + dedup configured.
QA + go-live
Live-fire test purchases across every funnel step. Meta EMQ verified at 8+. Tag Assistant + Pixel Helper passes. Side-by-side report delivered.
Verify accuracy
Your data flows clean. Within 7 days every signal — Meta, Google, TikTok, Microsoft — is fully accurate. Notion runbook + Loom walkthrough handoff.
Got questions?
The honestanswers.
No buzzwords, no upsell. If we don’t know, we say so.
01Why aren't my Firebase Auth conversions showing in PostHog?
Almost always because the distinct_id never reached the Firebase user identity. Anonymous authentication creates users before signup, and linking an anonymous account to a real one is a step teams frequently skip. Measure coverage before debugging the dispatch.
02What identifier does PostHog need?
PostHog identifies by distinct_id with an alias call to merge anonymous and identified users. On a self-hosted instance you also control the ingestion endpoint, which means the identifier survives ad blockers that would kill a third-party pixel — one of the few genuine technical advantages available to a first-party setup.
03Where should the event come from?
Your billing system, keyed on the user ID. Send paid conversions keyed on the user identity. Signups and anonymous sessions are stages, not revenue.
04How do I know it worked?
PostHog shows events in the activity view within moments. On a self-hosted instance, check the ingestion lag as well — events that are queued are not events that are lost, and the two need different responses.
Still have questions?Book a 30-min call— bring them all.
The call
What happens on your free 30-min call
No pitch deck, no SDR, no upsell pressure. Founder-led. Bring your ad-platform screens and yourFirebase Auth → PostHog setup — we’ll work through it together.
Min 1–5
We get the lay of your store
What you sell, what you spend on ads, who handles dev. Quick context-gathering — no questionnaire upfront.
Min 5–15
We audit your tracking live
Screen-share. We open your Meta Events Manager, GTM, and ad reports. You see exactly which conversions are leaking.
Min 15–25
We map a fix
What needs rebuilding, what stays. The exact Firebase Auth → PostHog setup we'd ship and what it would recover for you.
Min 25–30
Decide. Or don’t.
If we're a fit, we send a 1-page proposal in writing. If not, you walk away with a free remediation plan you can hand to anyone.
Get Firebase Auth and PostHog joined properly
Book a free 30-minute call. We measure your identifier coverage live on your own account, and you leave with a written plan — including the option that you don't need us.
Free · 30-min consultation · No commitment · Replies in under 2 hours · Available worldwide via WhatsApp
95% tracking accuracy guarantee
Free 30-min consultation · from $400 · 1st-party server-side
95% guarantee · from $400
