Last year, Mozilla announced that support for NPAPI plugins (except for Flash) would be ending in March 2017. That date is approaching fast, so I wanted to give folks more information about what’s happening. If you subscribe to my newsletter, this is the same information I gave there.

In short, Firefox 51 (which was released last week) is the last release of mainline Firefox that will support NPAPI plugins (except for Flash). Starting with Firefox 52, the only version of Firefox that will support plugins is the ESR. Firefox 52 WILL NOT have plugin support (except for Flash). Firefox 52 ESR WILL have plugin support.

That means that if your users are currently on Firefox 51 and you need plugin support, you need to switch Firefox so that it gets updates from the ESR channel. To do this, you need to change two files, channel-prefs.js and update-settings.ini.

In defaults/prefs/channel-prefs.js, change:

pref("app.update.channel", "release");

to

pref("app.update.channel", "esr");

In update-settings.ini, change:

ACCEPTED_MAR_CHANNEL_IDS=firefox-mozilla-release

to

ACCEPTED_MAR_CHANNEL_IDS=firefox-mozilla-esr

It is important that you make this change as close as possible to the release of Firefox 52 ESR (March 7, 2017), otherwise security updates to Firefox 51 will not be applied.

Plugin support will continue in the 52 ESR line only, meaning Firefox 59 will not have plugin support.

Some folks may ask why both Mozilla didn’t wait until Firefox 53 to deprecate plugins so that both versions of Firefox 52 would have the same capabilities. If they had done that, users who needed plugins would have had to downgrade to Firefox 52 ESR and that could cause incompatibilities with profiles. It made more sense to encourage people to switch to the same version (52 to 52 ESR).