Everything for the good of the users.
Mozilla announces that from next year, Firefox web browser users will lose one of three methods to install extensions. The company gives up the installation method of placing the XPI extension file in a special folder Firefox. This method was originally created for developers developing desktop applications, which were accompanied by extensions. They could configure the app installer file in such a way that it would leave an additional extension file in the said folder.
Why is Mozilla giving up this method of installing add-ons? The reason is security issues.
"Extensions installed in this way caused problems for users, because they often installed without their knowledge when installing other programs. Add-ons installed in this way could not be removed from the Add-ons Manager", said Caitlin Neiman from Mozilla.
The creators of Firefox hope that the change will help remove malware from many unofficial Firefox installers. Malware developers were eager to add extensions without users' knowledge thanks to the function of loading them from a folder and the ability to hide them in the Add-ons Manager. Starting with the release of Firefox 74 in March 2020, all extensions will be visible here, and "sideloading" will not be possible.