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I try to solve some caching issues I have with TBB. On websites which have hundreds of times the same image, TBB insists on re-downloading the image for every occurrence on the page even though the server correctly sets "expires", "max-age" and "cache control" headers. It does seem to respect the ETAGS and only gets a 304, but it still takes about 3 minutes to load a page like this.

I was looking to disable certain caching changes that might cause this but couldn't really find a reference for all the extensions.torbutton.xxx settings.

I only found this design documentation from 2011, but that seems outdated.

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The source code can be found here[1]. Regarding caching you have to be aware that it offers means to track users, just like a cookie. A server can send a header with a unique ETag to a client. Since the client will send that ETag in an If-None-Match header it can be tracked. Tracking a user makes it possible to create a profile which can theoretically lead to identification in the end. Also should a user ever (accidentally) reveal the identity it would just need an ETag or very specific (unique) max-age it could be a trace for all the actions a particular user did.

So by enabling caching you may significantly lower the bar for an attacker.

[1] https://gitweb.torproject.org/tor-browser.git/tree/

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