The organization revealed last month that it plans to only support WebExtensions in Firefox from the end of 2017 on.
If the schedule holds, Firefox 57 will only support WebExtensions and no longer classic add-ons. Te consequence is that add-ons that have not been ported won't be compatible with Firefox going forward.
There are reasons why Mozilla may delay making the cut when Firefox 57 is released; Firefox WebExtensions support is in active development right now. Some APIs are not complete, other features are not implemented yet, and some may not be on the radar at all right now.
Mozilla may also analyze how many add-ons will stop working when the change is made, and may decide to wait a bit longer to decrease that number.
One positive side effect of WebExtensions support in Firefox is that many Chrome extensions become compatible.
It is already possible to install many Chrome extensions in Firefox using a Firefox add-on called Chrome Store Foxified. Success depends largely on the version of Firefox, and the WebExtensions APIs it supports.
But how many Chrome extensions will run in Firefox?
Mozilla's Andy McKay decided to find out in November 2016. He parsed the Chrome store sitemap and got 100,000 extensions, apps and themes out of it which he analyzed to find out how many of them will run in Firefox.
According to his findings, about 76% of Chrome extensions of the sample size will run in Firefox. The remaining extensions either miss one or more APIs, one or more permissions, or one or more manifest.
There are some caveats however that need to be mentioned. First, that it does not mean that "compatible" extensions will run out of the box using Chrome Store Foxified. McKay notes that most should be easy to convert however to Firefox's format.
Other caveats mentioned are that the scan looked only at APIs, manifests and permissions, and not at other factors such as Web API support (which may be different). Also, API implementations may be different.
This figure will likely improve when Mozilla updates WebExtensions in the Firefox web browser though.
Firefox will drop support for a part of the add-ons that are currently available for the browser, yet it will gain support for Chrome extensions in the process.
It would be ideal obviously if Firefox would not lose any but gain support for Chrome nevertheless, at least for the foreseeable future.
Will the Chrome extensions be able to replace the lost functionality of Firefox add-ons that are no longer compatible with the browser? While that may be the case partially, Chrome extensions won't fill the gap completely as they can never offer what Firefox's previous add-ons system brought to the table.
Now You: Do you have Chrome extensions in mind that you would like to see in Firefox?