Firefox’s Private Browsing Mode enables users to browse the web privately. It empowers users to surf websites without storing browsing data (URLs, cookies, page content etc.). But, now Mozilla has discovered that Private Browsing Mode (PBM) in Firefox is partially broken, and browsing data get stored even if a user has enabled PBM.

According to a blog post ^[1] on official Mozilla Add-ons blog, this flaw generates because of Firefox Add-ons:

Add-ons have the ability to obtain and store browsing data, and some of these add-ons may not be taking PBM into account. This is a breach of the user’s privacy expectations when using PBM, so we will be updating our policies shortly, requiring add-ons to respect PBM.

Mozilla has announced to update user privacy policies soon. To overcome this problem, Mozilla has planned two different levelsof privacy support:

• If an add-on stores browsing data in any way, it must support PBM. This support cannot be disabled in any way.
• If an add-on stores some other type of personal data, support for PBM is optional.

In the referred blog post, Mozilla has suggested add-on developers to ensure PBM support for their add-ons. This is another issue discovered with Firefox add-ons recently. Few weeks ago, two experimental add-ons were found to be infected with trojans ^[2]. Although, later Mozilla informed that these reports were false.

Moreover, Google Chrome disables all extensions in PBM (incognito mode ^[3]).