4. Miscellaneous

4.1. How much does Privoxy slow my browsing down? This has to add extra time to browsing.

It should not slow you down any in real terms, and may actually help speed things up since ads, banners and other junk are not being displayed. The actual processing time required by Privoxy itself for each page, is relatively small in the overall scheme of things, and happens very quickly. This is typically more than offset by time saved not downloading and rendering ad images.

"Filtering" via the filterfile mechanism may cause a perceived slowdown, since the entire page is buffered before displaying. See below.

4.2. I noticed considerable delays in page requests compared to the old Junkbuster. What's wrong?

The entire page content must be loaded into memory in order for the filtering mechanism to work, and nothing is sent to the browser during this time. The loading time does not really change in real numbers, but the feeling is different, because most browsers are able to start rendering incomplete content, giving the user a feeling of "it works".

To modify the content of a page (i.e. make frames resizeable again, etc.) and not just replace ads, Privoxy needs to download the entire page first, do its content magic and then send the page to the browser.

4.3. What is the "http://p.p/"?

Since Privoxy sits between your web browser and the Internet, it can be programmed to handle certain pages specially.

With recent versions of Privoxy (version 2.9.x and greater), you can get some information about Privoxy and change some settings by going to http://p.p/ or, equivalently, http://config.privoxy.org/ (Note that p.p is far easier to type but may not work in some configurations. With the name change to Privoxy, this is changed from the previous http://i.j.b/ and earlier 2.9.x versions).

These pages are not forwarded to a server on the Internet - instead they are handled by a special web server which is built in to Privoxy.

If you are not running Privoxy, then http://p.p/ will fail, and http://config.privoxy.org/ will return a web page telling you you're not running Privoxy.

If you have version 2.0.2, then the equivalent is http://example.com/show-proxy-args (but you get far less information, and you should really consider upgrading to 2.9.15).

4.4. Do you still maintain the blocklists?

No, not by this name. The format of the blocklists has changed significantly in versions 2.9.x and later. This functionality is done by the "actions" file now. See next question ...

4.5. How can I submit new ads?

Please see the Contact section.

This process does not work with earlier versions of Privoxy or Junkbuster.

4.6. How can I hide my IP address?

You cannot hide your IP address with Privoxy or any other software, since the server needs to know your IP address to send the answers back to you.

Fortunately there are many publicly usable anonymous proxies out there, which solve the problem by providing a further level of indirection between you and the web server, shared by many people and thus letting your requests "drown" in white noise of unrelated requests as far as user tracking is concerned.

Most of them will, however, log your IP address and make it available to the authorities in case you abuse that anonymity for criminal purposes. In fact you can't even rule out that some of them only exist to *collect* information on (those suspicious) people with a more than average preference for privacy.

You can find a list of anonymous public proxies at multiproxy.org and many more through Google.

4.7. Can Privoxy guarantee I am anonymous?

No. Your chances of remaining anonymous are greatly improved, but unless you are an expert on Internet security it would be safest to assume that everything you do on the Web can be traced back to you.

Privoxy can remove various information about you, and allows you more freedom to decide which sites you can trust, and what details you want to reveal. But it's still possible that web sites can find out who you are. Here's one way this can happen.

A few browsers disclose the user's email address in certain situations, such as when transferring a file by FTP. Privoxy does not filter FTP. If you need this feature, or are concerned about the mail handler of your browser disclosing your email address, you might consider products such as NSClean.

Browsers available only as binaries could use non-standard headers to give out any information they can have access to: see the manufacturer's license agreement. It's impossible to anticipate and prevent every breach of privacy that might occur. The professionally paranoid prefer browsers available as source code, because anticipating their behavior is easier. Trust the source, Luke!

4.8. Might some things break because header information is being altered?

Definitely. More and more sites use HTTP header content to decide what to display and how to display it. There is many ways that this can be handled, so having hard and fast rules, is tricky.

"USER AGENT" in particular is often used in this way to identify the browser, and adjust content accordingly. Changing this now is not recommended, since so many sites do look for this. You may get undesirable results by changing this.

For instance, different browsers use different encodings of Russian and Czech characters, certain web servers convert pages on-the-fly according to the User Agent header. Giving a "User Agent" with the wrong operating system or browser manufacturer causes some sites in these languages to be garbled; Surfers to Eastern European sites should change it to something closer. And then some page access counters work by looking at the "REFERER" header; they may fail or break if unavailable. The weather maps of Intellicast have been blocked by their server when no "REFERER" or cookie is provided, is another example. There are many, many other ways things can go wrong when trying to fool a web server.

If you have problems with a site, you will have to adjust your configuration accordingly. Cookies are probably the most likely adjustment that may be required, but by no means the only one.

4.9. Can Privoxy act as a "caching" proxy to speed up web browsing?

No, it does not have this ability at all. You want something like Squid for this. And, yes, before you ask, Privoxy can co-exist with other kinds of proxies like Squid.

4.10. What about as a firewall? Can Privoxy protect me?

Not in the way you mean, or in the way a true firewall can, or a proxy that has this specific capability. Privoxy can help protect your privacy, but not really protect you from intrusion attempts.

4.11. The Privoxy logo that replaces ads is very blocky and ugly looking. Can't a better font be used?

This is not a font problem. The logo is an image that is created by Privoxy on the fly. So as to not waste memory, the image is rather small. The blockiness comes when the image is scaled to fill a largish area. There is not much to be done about this, other than to use one of the other "imageblock" directives: pattern, blank, or a URL of your choosing.

Given the above problem, we have decided to remove the logo option entirely [as of v2.9.13].

4.12. I have large empty spaces now where ads used to be. Why?

It would be easy enough to just eliminate this space altogether, rather than fill it with blank space. But, this would create problems with many pages that use the overall size of the ad to help organize the page layout and position the various components of the page where they were intended to be. It is best left this way.

4.13. How can Privoxy filter Secure (HTTPS) URLs?

This is a limitation since HTTPS transactions are encrypted SSL sessions between your browser and the secure site, and are meant to be reliably secure and private. This means that all cookies and HTTP header information are also encrypted from the time they leave your browser, to the site, and vice versa. Privoxy does not try to unencrypt this information, so it just passes through as is. Privoxy can still catch images and ads that are embedded in the SSL stream though.

4.14. Privoxy runs as a "server". How secure is it? Do I need to take any special precautions?

There are no known exploits that might effect Privoxy. On Unix-like systems, Privoxy can run as a non-privileged user, which is how we recommend it be run. Also, by default Privoxy only listens to requests from "localhost". The server aspect of Privoxy is not itself directly exposed to the Internet in this configuration. If you want to have Privoxy serve as a LAN proxy, this will have to be opened up to allow for LAN requests. In this case, we'd recommend you specify only the LAN gateway address, e.g. 192.168.1.1, in the main Privoxy config file. All LAN hosts can then use this as their proxy address in the browser proxy configuration. In this way, Privoxy will not listen on any external ports. Of course, a firewall is always good too. Better safe than sorry.

4.15. How can I temporarily disable Privoxy?

The easiest way is to access Privoxy with your browser by using the special URL: http://p.p/ and select "Toggle Privoxy on or off" from that page.

4.16. Where can I find more information about Privoxy and related issues?

Other references and sites of interest to Privoxy users:

http://www.privoxy.org/, the Privoxy Home page.

http://www.privoxy.org/faq/, the Privoxy FAQ.

http://sourceforge.net/projects/ijbswa/, the Project Page for Privoxy on SourceForge.

http://config.privoxy.org/, the web-based user interface. Privoxy must be running for this to work. Shortcut: http://p.p/

http://www.privoxy.org/actions/, to submit "misses" to the developers.

http://www.junkbusters.com/ht/en/cookies.html, an explanation how cookies are used to track web users.

http://www.junkbusters.com/ijb.html, the original Internet Junkbuster.

http://www.waldherr.org/junkbuster/, Stefan Waldherr's version of Junkbuster, from which Privoxy was derived.

http://privacy.net/analyze/, a useful site to check what information about you is leaked while you browse the web.

http://www.squid-cache.org/, a very popular caching proxy, which is often used together with Privoxy.

http://www.privoxy.org/developer-manual/, the Privoxy developer manual.