Mozilla Firefox provides third-party developers with a framework for writing extensions to add functionality to the browser. Extensions have unfettered access to browser privileges: extensions can snoop on web content, delete files from the hard drive, and even launch new processes from arbitrary binaries. Extensions might be intentionally malicious (i.e., a user unknowingly installs browser malware) or they might accidentally leak privileges to malicious web sites. It would be desirable to limit the powers of extensions, but we also do not want to cripple the extension framework too severely. Here, we review twenty-five "recommended" Firefox extensions to provide a basis for the discussion of legacy extensions' interface needs. Notably, we find that very few extensions need access to the file system or system calls despite the fact that all extensions have this ability.
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