Do these 3 things before closing this tab:
1Repair Windows errors before they cause bigger problems2Scan for outdated or missing drivers - takes under a minute3Clear out junk files and repair common Windows errorsiTechGuides is reader-supported. When you buy through links on our site, we may earn an affiliate commission. As an Amazon Associate I earn from qualifying purchases. Learn more
Use a Classic window for everyday browsing and sign-ins you want to keep, a Private window when you want Firefox to discard that session’s history and cookies after the last Private Window closes, and a Smart Window for supported tasks where AI assistance is useful and you’re comfortable sharing the context you choose. They serve different purposes: Private Browsing does not make you anonymous, and Smart Window can give incorrect answers.
Choose by what you need the window to do
| Your task | Best fit | Why |
|---|---|---|
| Routine browsing, saved sign-ins, and history you want available | Classic window | Site sessions and ordinary browsing history can remain available in Firefox. |
| A session you do not want retained in Firefox history or cookies afterward | Private Window | Firefox deletes session history, cookies, and site data after all Private Windows are closed. |
| Keep work and personal accounts signed in separately on the same site | Classic window with Multi-Account Containers | Containers separate site data by tab context and support multiple accounts on one site. |
| Get AI assistance with a task or referenced page | Smart Window, if available and appropriate | It can use context you refer to, so consider what you are sharing before using it. |
These are not three levels on a single privacy scale. Classic and Private primarily differ in what Firefox retains locally after a session; Containers separate account contexts; Smart Window adds an AI assistant.
What a Private Window does—and does not—keep
What Firefox removes
When you close every Private Window, Firefox removes that session’s browsing history, cookies, and site data from the device. This makes Private Browsing useful on a shared computer, for a fresh session with a site, or when you do not want a particular lookup saved in Firefox history. Mozilla describes the feature as privacy from other people who use the device, not anonymity online. Mozilla’s explanation of Private Windows covers the distinction.
What’s actually slowing this PC down?
Pick the symptom - the matching free tool is one click away.
What remains on the device
Files you download and bookmarks you create remain on the device. Private-session downloads are not retained in Firefox’s Downloads list after the session, but the downloaded files themselves are not automatically erased. Private Browsing is therefore not a way to leave no trace on a shared device.
#1 Best Overall
Who may still see your activity
Private Browsing does not hide your IP address or location. Websites, search engines, your internet provider, and an employer or school network may still observe activity. Signing in to an account can identify you to that service, and a Private Window does not protect against spyware or keyloggers already on the device. Firefox’s page-safety and malware protections are not exclusive to Private Windows. See Mozilla’s Private Browsing guide for more detail.
Why ads can still appear
Private Browsing blocks known trackers, but a tracker is not the same thing as every advertisement. A site may show contextual ads based on the page you are viewing, or ads associated with an account where you are signed in. A Private Window should not be treated as an ad blocker.
Classic windows are not automatically unprotected
A Classic window is the normal choice when you want history and site sessions to remain available. Firefox’s Enhanced Tracking Protection applies in Classic windows too, and Total Cookie Protection is available there. The exact blocking depends on your tracking-protection setting: Mozilla says Standard mode confines cookies by site and limits tracking-content blocking to Private Windows, while Strict mode extends blocking to all windows and includes bounce-tracking protection. Mozilla’s desktop Enhanced Tracking Protection guide explains the settings.
Quick wins for a faster PC:
Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →Private Windows also hide some additional identifying details, and Firefox blocks companies whose business is fingerprinting in every window. Private Windows send Global Privacy Control automatically, but a website’s response depends on the site and applicable law. These protections reduce some forms of tracking; they do not make browsing anonymous.
Use Containers when the goal is separate accounts
If you need to stay signed in to more than one account on the same site, Multi-Account Containers in a Classic window are a better fit than Private Browsing. Mozilla’s Containers feature lets you open color-coded contexts such as Work, Banking, Shopping, and Personal, each with separate site data. It is designed to keep those contexts distinct while allowing multiple accounts on one site. Containers are disabled in Private Browsing windows. Read Mozilla’s Multi-Account Containers guide for its setup and behavior.
Use Smart Window selectively for AI assistance
Smart Window uses a large language model (LLM) to assist with supported tasks. Depending on what you ask, it may consider the current page, open tabs you reference, or history you explicitly ask about; Private Window activity is inaccessible to it. Treat page contents and browsing context as information you are choosing to share, particularly if they are sensitive. Mozilla says requests pass through a proxy so the AI service does not see your unique Firefox/browser identifier or IP address. Conversations are not collected or stored for training or human review unless you opt in.
AI answers can be wrong or misleading. Mozilla describes safeguards but cautions that harmful outcomes cannot be completely prevented. Verify consequential claims using reliable sources rather than treating an AI response as authoritative. Details are in Mozilla’s Smart Window safety and privacy information and getting-started guide.
Recommended Free Tools
Availability depends on location and Firefox version
Smart Window is a rollout, not a feature to assume every Firefox user has. Mozilla’s safety page says rollout starts in the US and Canada with Firefox 150, and in France with Firefox 155. Availability outside those stated regions and versions is not established by that rollout note; check Firefox’s current interface and Mozilla’s support information for your location.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.A quick decision checklist
- Want ordinary history and persistent sign-ins? Open a Classic window.
- Want Firefox to discard session history, cookies, and site data after you finish? Use a Private Window, then close all Private Windows.
- Need separate work and personal accounts at once? Use Multi-Account Containers in a Classic window.
- Want AI help? Use Smart Window only if it is available and the page or account context is appropriate to share.
If your main concern is who can see activity, distinguish local device history from network or website visibility: Private Browsing changes the former, not the latter.
Related Firefox details
Extensions do not necessarily behave the same way in Private Browsing as in Classic windows. Mozilla explains how to allow or manage them in its guide to extensions in Private Browsing.
Quick Recap
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
