An updated Firefox package has been released for Ubuntu 14.04 LTS, 16.04 LTS, and 17.04 to address a performance regression with WebExtensions that was introduced in the previous update.

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Ubuntu Security Notice USN-3391-3
August 17, 2017

firefox regression
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A security issue affects these releases of Ubuntu and its derivatives:

- Ubuntu 17.04
- Ubuntu 16.04 LTS
- Ubuntu 14.04 LTS

Summary:

USN-3391-1 introduced a regression in Firefox.

Software Description:
- firefox: Mozilla Open Source web browser

Details:

USN-3391-1 fixed vulnerabilities in Firefox. The update introduced a
performance regression with WebExtensions. This update fixes the problem.

We apologize for the inconvenience.

Original advisory details:

Multiple security issues were discovered in Firefox. If a user were
tricked in to opening a specially crafted website, an attacker could
potentially exploit these to conduct cross-site scripting (XSS) attacks,
bypass sandbox restrictions, obtain sensitive information, spoof the
origin of modal alerts, bypass same origin restrictions, read
uninitialized memory, cause a denial of service via program crash or hang,
or execute arbitrary code. (CVE-2017-7753, CVE-2017-7779, CVE-2017-7780,
CVE-2017-7781, CVE-2017-7783, CVE-2017-7784, CVE-2017-7785, CVE-2017-7786,
CVE-2017-7787, CVE-2017-7788, CVE-2017-7789, CVE-2017-7791, CVE-2017-7792,
CVE-2017-7794, CVE-2017-7797, CVE-2017-7798, CVE-2017-7799, CVE-2017-7800,
CVE-2017-7801, CVE-2017-7802, CVE-2017-7803, CVE-2017-7806, CVE-2017-7807,
CVE-2017-7808, CVE-2017-7809)

Update instructions:

The problem can be corrected by updating your system to the following
package versions:

Ubuntu 17.04:
firefox 55.0.2+build1-0ubuntu0.17.04.1

Ubuntu 16.04 LTS:
firefox 55.0.2+build1-0ubuntu0.16.04.1

Ubuntu 14.04 LTS:
firefox 55.0.2+build1-0ubuntu0.14.04.1

After a standard system update you need to restart Firefox to make
all the necessary changes.

References:
https://www.ubuntu.com/usn/usn-3391-3
https://www.ubuntu.com/usn/usn-3391-1
https://launchpad.net/bugs/1710987

Package Information:
https://launchpad.net/ubuntu/+source/firefox/55.0.2+build1-0ubuntu0.17.04.1
https://launchpad.net/ubuntu/+source/firefox/55.0.2+build1-0ubuntu0.16.04.1
https://launchpad.net/ubuntu/+source/firefox/55.0.2+build1-0ubuntu0.14.04.1

  Firefox Regression Update For Ubuntu