"Mozilla has started to distribute two new system add-ons for Firefox 49.0 and Firefox 49.0.1 to address two issues affecting Adobe Flash Player and graphics issues.
"The organization is working on Firefox 49.0.2 currently, but made the decision to release two new patches for the current stable version of Firefox as system add-ons to address issues that users are affected by.
"System add-ons are like hotfixes. They can be pushed out to all Firefox users who have automatic updates enabled to fix issues of the browser. That's usually a lot faster than having to create a new build of Firefox.
"The two system add-ons address two issues in Firefox 49 and 50. ..."

Source: gHacks Tech News
 Firefox 49: two new system add-ons to fix Flash and graphics issues