If you click "more" on your add-ons, you can see the version of the add-on. And legacy is termed as ... Add-ons built with the old technology are labeled “Legacy” in the Add-ons Manager (about:addons) tab.

taken from : https://support.mozilla.org/en-US/kb/firefox-add-technology-modernizing?as=u&utm_source=inproduct

moderator note: fixed text formatting for readability

There are two kinds of extensions. Old XUL based extensions are marked as 'Legacy' and these legacy extensions will be phased out in 55 and 56 and disabled in Firefox 57+. The new extensions are named WebExtensions and are marked as 57+ compatible on the Add-ons website.

• https://www.ghacks.net/2016/11/24/firefox-will-only-support-web-extensions-by-the-end-of-2017/

It means that Firefox is limiting the ability for others to control their user interface experience on Firefox. Very shameful that FF is becoming more like the other "big browsers." What has distinguished FF is the ability to customize the browser's interface.

I have been using Vivaldi browser for a week now. I am beginning to prefer it. I remember updating to FF1.6. (2003?) I can't see myself going back to Firefox, sad really Oh well, bye bye

It is quite likely that more and more (all?) legacy extensions will be removed from the Add-ons website at some point, so you won't be able to install them and they won't be updated anymore.

• https://blog.mozilla.org/addons/2017/02/16/the-road-to-firefox-57-compatibility-milestones/

Very disappointed with this 14 of my 19 extensions are listed as Legacy

I have 11 extensions and only 2 of them aren't legacy. For years I have refused to even try Chrome because I couldn't get Tab Mix Plus as an addon. Guess what is a legacy? Tab Mix Plus. If it can't get that, a flash blocker, and auto unload tab extension, Live Click and a decent session manager then I won't upgrade. I want the Classic Theme restorer, but I could force myself to live without it.

I really hope Mozilla rethinks this move.

You can follow the progress:

• bug 1226546 - [tracking] Support Tab Mix Plus as a webextension

Please do not comment in bug reports
https://bugzilla.mozilla.org/page.cgi?id=etiquette.html

You can vote for a bug to show your interest
https://bugzilla.mozilla.org/page.cgi?id=voting.html

I recently switched to Vivaldi browser, which I am quite impressed with, took me about a week to discover how to use it properly, there is still some stuff I haven't found out about. I started with Firefox around 2003 and remember the excitement each time there was an upgrade. Now I just think ho hum, nothing seems to have changed apart from one extension after the other disappearing. I will let Firefox upgrade, most of my extensions are labelled 'Legacy'. Unless there is a a work around of some kind, and I don't mean Nightly, I shall not be using it any more. I have seen a few really arrogant responses from the FF team concerning average users like me when we dare to criticise, I don't see much point in continuing with FF.

Hi cooked, I think everyone has their own opinion on the loss of legacy add-ons that can't be fully replaced. There are security/performance reasons for it, but we'll miss them all the same.

As you probably know, support forum contributors and other members of the Mozilla community do not speak for Mozilla. So if a person seems arrogant (or even especially nice), I wouldn't ascribe it to the organization as a whole or to other community members.

jscher2000 said

Hi cooked, I think everyone has their own opinion on the loss of legacy add-ons that can't be fully replaced. There are security/performance reasons for it, but we'll miss them all the same. As you probably know, support forum contributors and other members of the Mozilla community do not speak for Mozilla. So if a person seems arrogant (or even especially nice), I wouldn't ascribe it to the organization as a whole or to other community members.

It was a Mozilla developer that gave me that imprtession.

cor-el said

There are two kinds of extensions. Old XUL based extensions are marked as 'Legacy' and these legacy extensions will be phased out in 55 and 56 and disabled in Firefox 57+. The new extensions are named WebExtensions and are marked as 57+ compatible on the Add-ons website.

• https://www.ghacks.net/2016/11/24/firefox-will-only-support-web-extensions-by-the-end-of-2017/

Apparently FF developers are incapable of writing a functional browser and continue to degrade the ability of the user keeping FF working after spending hours of getting it to the point where they like it. I personally will be dropping back to ver 53 and blocking any further updates.

If nobody uses this browser, there won't be any security issues.

I'll be honest. I've been using Firefox for almost ten years, and I've seen it get slower and slower. I was using the ESR releases for a bit, but they seem behind. The 64-bit Firefox is pretty smooth. But, this ending support for extensions is a real issue. I have a security camera system that needs an extension. Legacy. I have an addon for large print because I am visually impaired. Legacy. I understand these addon methods may be old and not 100% secure, but Mozilla needs to understand that some users, like me and many other of you on here, have a LOT of addons that we depend upon. Disable legacy addons but have an option to turn them on IF a user needs them. I'm a tech of 16 years. I know how to browse safely. It's like Android phones that they won't let you root.

Hi mrsubway, I've never heard of a security camera requiring an extension. What does it do??

For large print, perhaps there will be a replacement. Do you want to mention which one it is?

Some future releases of Firefox will be able to run some (not all) legacy extensions. At this time, that would be the Developer Edition (a variation on Firefox Beta) and Nightly (the cutting edge). https://www.mozilla.org/firefox/channel/desktop/

This Legacy issue was the last straw. I tried a few Browsers - IE, Chrome, Edge and Vivaldi. All were substantially faster than Firefox and none had the continuing script error that dogged Firefox. I settled on Vivaldi as it had the user interface that most resembled Firefox. Also, since it is a close cousin to Chrome, extensions designed for Chrome also work on Vivaldi.

duhnel said

This Legacy issue was the last straw. I tried a few Browsers - IE, Chrome, Edge and Vivaldi. All were substantially faster than Firefox and none had the continuing script error that dogged Firefox. I settled on Vivaldi as it had the user interface that most resembled Firefox. Also, since it is a close cousin to Chrome, extensions designed for Chrome also work on Vivaldi.

I have been a FF user for ever, but I agree the legacy issue may have done it for me, along with continuing crashes of ver. 56.

I have Comodo Ice Dragon on my desktop and will likely make it my default. It's a virtual clone of my FF setup, ALL of my add-ons will work (no legacy box showing up) and it uses a little more than half the memory of FF 56.

I discovered the Steve2526 post today and installed Comodo IceDragon I will use this I was trialing Opera as I new it had Fireshot which is a must have for me but it is very primitive in Opera. When setting it up it imported everything from FF so quick to go with my book marks added the extensions you wouldn't know it has a different brand name.

ron525 said

I discovered the Steve2526 post today and installed Comodo IceDragon I will use this I was trialing Opera as I new it had Fireshot which is a must have for me but it is very primitive in Opera. When setting it up it imported everything from FF so quick to go with my book marks added the extensions you wouldn't know it has a different brand name.

Agreed, sort of. I added IceDragon to my startup programs and low and behold, I got a black screen. After going through another restart I managed to get into safe restart without Internet and then uninstalled Commodo Cloud antivirus and Comodo internet security. It seems that my existing antivirus program (Windows Defender and Antispyware) conflicts with Commodo. A bit mean not to mention this. However I must say that it is a nice browser and I haven't given up on it yet.

cooked said

ron525 said

I discovered the Steve2526 post today and installed Comodo IceDragon I will use this I was trialing Opera as I new it had Fireshot which is a must have for me but it is very primitive in Opera. When setting it up it imported everything from FF so quick to go with my book marks added the extensions you wouldn't know it has a different brand name.

Agreed, sort of. I added IceDragon to my startup programs and low and behold, I got a black screen. After going through another restart I managed to get into safe restart without Internet and then uninstalled Commodo Cloud antivirus and Comodo internet security. It seems that my existing antivirus program (Windows Defender and Antispyware) conflicts with Commodo. A bit mean not to mention this. However I must say that it is a nice browser and I haven't given up on it yet.

Nope I had to completely remove every trace of icedragon from my computer and mess around with the F12 key to get things to work again (countless retarts) Not worth the panic, I'm sticking with Vivaldi