Mozilla Tabstack
SafeUser-agent: Mozilla-Tabstack
Category: AI & LLM Bots
SEO impact if blocked: 2/10
Mozilla
1 crawler operated by Mozilla
https://www.mozilla.org/Who Mozilla is, for site owners
Mozilla operates 1 crawler in our directory, filed under AI & LLM Bots. Its crawl behaviour is rated safe.
Blocking Mozilla carries an SEO impact score of 2/10. Blocking impact is rated: Low - No SEO ranking impact.
Our recommendation for Mozilla: Generally safe to allow; provides legitimate crawling value.
Mozilla at a glance
| Operator | Mozilla |
|---|---|
| Crawler in directory | 1 |
| Categories | AI & LLM Bots |
| SEO impact if blocked | 2/10 |
| Crawl behaviour | 1 rated safe |
| Website | www.mozilla.org |
| Official crawler docs | Mozilla crawler documentation |
Crawler operated by Mozilla
What Mozilla's crawlers are for
Mozilla runs 1 crawler in our database. Grouped by the job each one does:
- a user-triggered agent:
Mozilla-Tabstack
The highest-priority token is Tier 2. That puts Mozilla among the operators whose crawlers have a direct effect on whether AI answers or search results can include your pages.
How site owners treat Mozilla
None of Mozilla's tokens were among the names tracked in our robots.txt study of the Tranco top 10,000, which usually means few large sites write rules for them yet. Your own logs are the best evidence of how often they visit.
Writing one policy for Mozilla
A robots.txt file cannot say "Mozilla"; it can only name Mozilla's tokens, one group at a time. With a single token, one group is the whole policy.
# One token controls everything Mozilla fetches through it
User-agent: Mozilla-Tabstack
Disallow: /private/
Allow: /- Decide per job, not per company. Training, search and user-triggered fetching have different trade-offs, even from the same operator.
- Name every token you mean. A token you leave out follows
User-agent: *. - Repeat shared rules. A named group ignores the
*group, so copy anyDisallowlines you still want it to obey. - Verify from outside. Run the live AI crawler test after any change to see the result for each Mozilla token, including firewall refusals.
Test yourself: does User-agent: Mozilla block all of Mozilla's crawlers?
No. robots.txt matches crawler tokens, not company names. Use the token Mozilla-Tabstack.
Test yourself: if you block one Mozilla token, are the others blocked too?
No. Each token is read separately. Blocking one leaves the rest following whatever group applies to them.
Each Mozilla crawler, explained
A one-paragraph brief for every Mozilla token in our database, covering what it does, how it treats robots.txt and how often large sites write rules for it:
- Mozilla Tabstack (
Mozilla-Tabstack, Tier 2): a user-triggered agent that fetches a page when a person asks an assistant or app to open it. Rated safe. Mozilla Tabstack's operator does not clearly document how it treats robots.txt. Write the Mozilla Tabstack rule anyway, then confirm in your logs that its requests stop. Not tracked in our robots.txt study.
Common mistakes with Mozilla's crawlers
The errors we see most often with Mozilla's crawlers in the files and firewalls we test:
- Assuming a robots.txt rule will stop Mozilla's crawlers. User-triggered fetches act for a person, and some operators say robots.txt may not apply to them. Check the operator's statement above.
- Blocking Mozilla's crawlers as if it were a bulk crawler. It fetches one page because a person asked; blocking it means that person's assistant cannot read your page.
- Counting Mozilla's crawlers visits as crawl volume. Each request maps to a real user question, which makes the paths it requests a useful signal of what people ask about you.
All three hide inside a file that looks correct, so check Mozilla's crawlers from outside after every change.
What our own data shows about Mozilla
Everything below comes from the AI Crawler Check bot database and our two most recent robots.txt scans of the Tranco top 10,000, not from Mozilla's marketing. Mozilla has one token in our database, so the whole picture fits in one place.
Mozilla-Tabstack in our records
We first recorded Mozilla-Tabstack on September 22, 2026. Mozilla documents it on docs.tabstack.ai, and we recheck that page before each release. No file in our top-10,000 scans names Mozilla-Tabstack, so any rule you write for it puts you ahead of almost every large site.
Among the 104 AI and LLM crawlers in our database, Mozilla-Tabstack sits 69th by priority (Tier 2), level with AddSearchBot, AI2Bot, AI2Bot-DeepResearchEval, aiHitBot. 81 of the 104 share its safe rating. Other operators with a crawler that fetches a page when a person asks an assistant or app to open it: ChatGPT Agent (OpenAI, Tier 1), ChatGPT Operator (OpenAI, Tier 1), ChatGPT-User (OpenAI, Tier 1), ChatGPT-User/2.0 (OpenAI, Tier 1), Claude-SearchBot (Anthropic, Tier 1). A policy for Mozilla-Tabstack is usually a policy for these too.
A decision record for Mozilla-Tabstack
Teams that review crawlers once a quarter keep one short entry per token, so anyone can see why a rule exists and when it was last checked. Filled in from our data, the Mozilla-Tabstack entry reads:
- Operator and job: Mozilla; it fetches a page when a person asks an assistant or app to open it.
- Priority and behaviour: Tier 2, rated safe, blocking impact low.
- Suggested starting point: Allow, and watch it in your logs.
- Enforcement: Mozilla-Tabstack's operator does not clearly document how it treats robots.txt. Write the Mozilla-Tabstack rule anyway, then confirm in your logs that its requests stop.
User-agent: Mozilla-Tabstack
Allow: /Paste the line into the validator with one of your own URLs before it goes live. Revisit the Mozilla-Tabstack entry whenever Mozilla announces a change, because a Tier 2 crawler affects visibility directly.
Checking Mozilla-Tabstack on your own site
Because Mozilla runs only Mozilla-Tabstack in our records, one check covers the whole operator. Search your access logs for the string Mozilla-Tabstack over the last 30 days, note how many requests it made and which paths it asked for, then compare that with what your robots.txt allows. Match the requests against what Mozilla publishes about the crawler, since that page is the only authority on its behaviour. A Tier 2 crawler rated safe is worth confirming every month, and our log checker does the counting for you.
How top sites treat Mozilla's crawlers
From our robots.txt study of the Tranco top 10,000 (5,583 valid files, fetched October 20, 2026):
None of the tokens for Mozilla's crawlers is tracked by name in our study. For scale, 20.1% of top-site files block at least one AI training crawler and 4.3% refuse every unnamed crawler with User-agent: * and Disallow: /, which would catch Mozilla's crawlers too.
More questions about Mozilla
- Will blocking Mozilla affect my Google rankings?
- Only if one of its tokens is a Google search crawler. None of Mozilla's tokens are Googlebot, so classic Google rankings are unaffected.
- How quickly does a robots.txt change take effect for Mozilla?
- Crawlers cache robots.txt, commonly for up to a day. Expect a change to apply within about 24 hours, and confirm it in your logs.
- Can I allow Mozilla on some sections and block it on others?
- Yes. Inside the group for
Mozilla-Tabstack, addDisallowlines for the paths to keep private andAllowlines for exceptions. The longest matching rule wins. - Does blocking Mozilla delete content it already collected?
- No. robots.txt only controls future visits. For content already collected, check whether Mozilla offers a removal or opt-out process.
- Is a firewall block better than robots.txt for Mozilla?
- A firewall enforces the decision, while robots.txt asks politely. Many operators recommend robots.txt because blocking their IPs can stop them reading your rules at all. Use robots.txt first, and add a firewall rule only if requests continue.
A five-minute Mozilla review
- Confirm the token. Compare the user-agent in your logs with the tokens listed on this page. A close spelling is not the same crawler.
- Decide the outcome per crawler. Use the briefs above to choose allow, limit or block for each token.
- Write the group. Add or edit one
User-agentgroup per decision and repeat any shared rules inside it. - Publish and wait. Allow about a day for crawlers to fetch the new file.
- Confirm the result. Check your logs, then run the robots.txt AI crawler test to see the outcome from outside, including any firewall layer.
How to block or allow Mozilla in robots.txt
This rule covers the single crawler Mozilla operates. Add it to the robots.txt file at the root of your domain.
Block Mozilla completely
User-agent: Mozilla-Tabstack
Disallow: /
Allow Mozilla explicitly
User-agent: Mozilla-Tabstack
Allow: /
These Mozilla rules ask; they do not enforce. If a Mozilla token ignores them, block it at the server or CDN. Paths are case-sensitive, and each rule matches the token, not the full user-agent string.
Frequently asked questions about Mozilla
What crawler does Mozilla run?
Mozilla operates 1 crawler in our directory: Mozilla Tabstack (user-agent Mozilla-Tabstack).
Should I block Mozilla?
Generally safe to allow; provides legitimate crawling value. The SEO impact score for blocking is 2/10, where 10 means blocking costs you the most visibility.
How do I block Mozilla in robots.txt?
Add the following to robots.txt at your domain root: User-agent: Mozilla-Tabstack then Disallow: /.
Does blocking Mozilla hurt my search rankings?
Blocking impact is rated: Low - No SEO ranking impact. Google's own ranking crawler is Googlebot, which this operator does not run, so blocking Mozilla does not by itself remove you from Google's index. What it can change is whether AI assistants and analytics tools can read your pages.