USN-3645-1 fixed vulnerabilities in Firefox. The update caused an issue where users experienced long UI pauses in some circumsances.
This update fixes the problem.

We apologize for the inconvenience.

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 cause a denial of service via application crash, bypass same-origin restrictions, conduct cross-site scripting (XSS) attacks, install lightweight themes without user interaction, spoof the filename in the downloads panel, or execute arbitrary code.
(CVE-2018-5150, CVE-2018-5151, CVE-2018-5153, CVE-2018-5154, CVE-2018-5155, CVE-2018-5157, CVE-2018-5158, CVE-2018-5159, CVE-2018-5160, CVE-2018-5163, CVE-2018-5164, CVE-2018-5168, CVE-2018-5173, CVE-2018-5175, CVE-2018-5177, CVE-2018-5180)

Multiple security issues were discovered with WebExtensions. If a user were tricked in to installing a specially crafted extension, an attacker could potentially exploit these to obtain sensitive information, or bypass security restrictions. (CVE-2018-5152, CVE-2018-5166)

It was discovered that the web console and JavaScript debugger incorrectly linkified chrome: and JavaScript URLs. If a user were tricked in to clicking a specially crafted link, an attacker could potentially exploit this to conduct cross-site scripting (XSS) attacks. (CVE-2018-5167)

It was discovered that dragging and dropping link text on to the home button could set the home page to include chrome pages. If a user were tricked in to dragging and dropping a specially crafted link on to the home button, an attacker could potentially exploit this bypass security restrictions. (CVE-2018-5169)

It was discovered that the Live Bookmarks page and PDF viewer would run script pasted from the clipboard. If a user were tricked in to copying and pasting specially crafted text, an attacker could potentially exploit this to conduct cross-site scripting (XSS) attacks. (CVE-2018-5172)

It was discovered that the JSON viewer incorrectly linkified javascript: URLs. If a user were tricked in to clicking on a specially crafted link, an attacker could potentially exploit this to obtain sensitive information. (CVE-2018-5176)

It was discovered that dragging a file: URL on to a tab that is running in a different process would cause the file to open in that process. If a user were tricked in to dragging a file: URL, an attacker could potentially exploit this to bypass intended security policies. (CVE-2018-5181)

It was discovered that dragging text that is a file: URL on to the addressbar would open the specified file. If a user were tricked in to dragging specially crafted text on to the addressbar, an attacker could potentially exploit this to bypass intended security policies.
(CVE-2018-5182).

Note that Tenable Network Security has extracted the preceding description block directly from the Ubuntu security advisory. Tenable has attempted to automatically clean and format it as much as possible without introducing additional issues.

Ubuntu 14.04 LTS / 16.04 LTS / 17.10 / 18.04 LTS : Firefox regression (USN-3645-2)

critical Nessus Plugin ID 109940

No changelogs found