The most recent version of Firefox Nightly, the browser's cutting edge version, highlights the add-ons that are not WebExtensions with the Legacy tag.
One of the concerns that Firefox users who run one or multiple add-ons in the browser have currently is whether their add-ons will make the cut when Firefox 57 comes along.
It is in this version of Firefox, out November 2017, that Mozilla plans to drop support for so-called legacy add-ons.
The move blocks any non-WebExtension add-ons from working in the browser. In fact, users won't be able to install legacy add-ons when Firefox 57 hits, and the add-ons that they had installed before the upgrade to the new version of the browser won't be there anymore after the upgrade.
It is a clear cut that Mozilla plans, one that is welcome by some and disliked by others. For Mozilla, moving Firefox's extensions system to WebExtension exclusively means a reduction in extension caused crashes and performance issues, the freeing up of development time because extension compatibility is less of an issue, and that users won't face that many issues anymore caused by add-ons.
The naysayers of the move point out that Firefox will lose part of its add-on ecosystem, and with it add-ons. Extension won't be as powerful anymore, and are restricted in what they can do as they rely solely on the APIs that Mozilla creates. Some features that legacy add-ons offered are simply not implementable with the new WebExtensions system.
Firefox users who run add-ons currently are also concerned when it comes to the add-ons that they are using in the browser. Will those make the cut, or won't they?
It was quite difficult up until now to come up with an answer. The release of the latest Firefox Nightly version changes that, as legacy add-ons are tagged as that in the browser's add-on manager.
If you want to verify whether your add-ons will make the cut if the cut would happen today, do the following (only in Firefox Nightly currently):
- Load about:addons in the Firefox address bar.
- Firefox should highlight all legacy add-ons right in the interface.
Note: If you run Classic Theme Restorer, or another add-on that modifies the browser UI, you may not see the legacy tag there. You may see it with a click on the more link though.
- Click on the "more" link next to an add-on.
- Firefox displays Legacy next to the add-on if it is a legacy add-on.
Please note that some developers are working on porting their extensions to the WebExtensions system. While these may be listed as legacy currently, they may be released as WebExtensions before the cut so that you may continue using them.
Still, the tagging of add-ons as legacy makes a whole lot of sense. Mozilla should, and probably will, move the tagging to Beta and Stable versions of Firefox in the near future.