The problem may be the add-on is not compatible to your Firefox.

What's your computer system and Firefox version?

What add-ons are you talking about?

Just to be sure, you are viewing your Extensions on the Add-on page? Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons
• type or paste about:addons in the address bar and press Enter/Return

In the left column of the Add-ons page, click Extensions.

In the list on the right side, if the extension does not have an Enable button (or similar term) then there may be one of the following problems:

• The extension is not digitally signed by the Add-ons team -- usually this will say something about the extension not being verified (see: Add-on signing in Firefox)
• The extension is incompatible with multiprocess -- try updating the extension using the small "gear" button above the list, then on that little menu, Check for Updates, to see whether a compatibility update is available
• The extension is blocked because it causes severe crashing -- there may be specific information on the extension's details page when you click its More link on the Add-ons page
• If you are using Firefox Beta, which is Firefox 57, "Legacy" extensions can no longer be enabled

If you have a question about a specific extension, can you mention which one it is?

Hi,

I know that this extension isn't supported in Firefox 57 but I want to know if I can force the use before change to ESR and block the updates.

Thanks

Force it how?? If it is labeled "Legacy" I think it can only be enabled in the "Developer" Edition or in "Nightly" and it's not guaranteed to work. (There is something you change in about:config in those versions.)

https://www.mozilla.org/firefox/channel/desktop/

Also, if you switch to ESR, you do not need to block updates because ESR is going to remain on Firefox 52 until around June 2018.

How can I change it in Nightly and Developer for make it work? If I enable it in the ESR, when I launch Beta it auto deactivate the extension.

Thanks

antonio8909 said

How can I change it in Nightly and Developer for make it work? If I enable it in the ESR, when I launch Beta it auto deactivate the extension.

You need to run multiple versions of Firefox on the same computer? Generally speaking, it is best to create separate profiles in that case because the older versions can have problems with the changes made by newer versions. More information:

• Profile Manager - Create, remove or switch Firefox profiles
• http://kb.mozillazine.org/Using_multiple_profiles_-_Firefox

Regarding the preference in about:config I don't remember what it's called. You may find the information on Reddit where many Developer Edition and Nightly users have been discussing Firefox 57 for the past two months: https://www.reddit.com/r/firefox/

I followed that steps in https://support.mozilla.org/en-US/kb/profile-manager-create-and-remove-firefox-profiles but it still disable the extension in ESR... :(

You need to change how your ESR and Beta start so they do not use the same profile. Please see the other article I linked. Or change it every time, your choice.

Note that a lot of code used by legacy extensions is going to be removed, so even if you can activate the extension in DE then it isn't guaranteed that it will keep working.

• extensions.legacy.enabled = true

• Bug 1347507 - Stuff we can remove when XPCOM extensions are no longer supported

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

I managed to create another profile with another shortcut but I don't understand why I can't enable old extensions in Firefox Beta... Anyway I selected ESR to stop searching updates. I'm not going to update that version ever...

In case that anyone is thinking about what extension I need: https://addons.mozilla.org/en-us/firefox/addon/hls-stream-detector/?src=search The developer doesn't want to port it to WebExtensions so that's why I need to have another version of Firefox because I don't want to lose that extension.

You can't enable old extensions in Beta and Release builds. That is only possible in Developer Edition and Nightly builds.

cor-el dijo

You can't enable old extensions in Beta and Release builds. That is only possible in Developer Edition and Nightly builds.

It doesn't work in Developer/Nightly

cor-el, can you explain me hoe to enable it in Developer? I'll try it again.

Thanks

What extensions is this about? Isn't there any Legacy extension that works?

With extensions.legacy.enabled set to true you should at least see them under extensions.

Did you check the Browser Console for messages?

• https://developer.mozilla.org/en/Tools/Browser_Console