Disable Firefox synchronisation for a single addon

Question

I use firefox sync on different pcs and have an addon that should only be synct/enabled on one of them. How can this be realized?

Background: Zoom

One of my pcs is connected to my TV. It's used to surf on the web, watch videos, play games and so on. 100% zoom can be hard to read on some websites. Since firefox can't zoom globally, I recently installed NoSquint Plus for this. It works well, but now I'm sitting on my main pc and I now have 120% zoom here, too. This is caused by the sync and doesn't make sense for a regular computer on the table.

I don't want disable the sync for all addons because it's usefull for other ones, that I use on all pcs. The perfect solution would be the ability to disable firefox sync only on NoSquint Plus. Sadly I can't find any setting to choose which addons should synchronize.

Possible workaround

Set services.sync.addons.ignoreUserEnabledChanges to true (source: Firefox wiki) and disable the addon on all other machines. With the side effect, that changes to other addons must be applied individually on all machines. And it could be hard to troubleshoot, if I'm wondering about this behavior in the future.

Answer 1

In earlier versions of Firefox, you could open multiple instances of Firefox using different profiles. Profiles can contain different collections of add-ons, and synching can be turned on and off by profile. Unfortunately, it looks like you now can't get to the profile manager while an instance of Firefox is open. So that kind of rules out controlling this with profiles. But here's another idea for you:

It doesn't matter whether an add-on is installed if it is disabled; a disabled add-on doesn't affect anything except using a little disk space for its existence.

Install NoSquint Plus on the one device where you need it. On that computer, keep synching turned off except when you run it manually by temporarily turning it on. Create a reminder system for yourself to manually synch that computer on whatever schedule you want, and follow this procedure:

• Disable NoSquint Plus (button on the add-ons page) while you synch that computer.
• Turn on synching and wait for it to finish. Synching may add NoSquint Plus to other computers when they synch (not all add-ons get added), but if it is, it will be added in a disabled state, and won't affect the other computers.
• When synching is complete, turn it off on that computer and re-enable NoSquint Plus.

So you have a minor manual synching procedure on that one computer. If you mess up and accidentally synch without disabling NoSquint Plus, you can disable it and resynch, which will update the database, hopefully before other computers synch. But worst case, if you end up with an enabled version on any other computers, just go into add-ons and disable or remove it there. As long as you follow the procedure, you can synch without having the other computers affected.

Answer 2

The latest Firefox version supports Add-on Collections, which offer an alternative way of syncing add-ons. Instead of syncing all add-ons, you create your own collection of them and use it.

Collections let you save and share lists of add-on listings on addons.mozilla.org and subscribe to them through a URL.

For more information see the Mozilla article Collections and User Profiles have a new look.
As I'm not using this feature, you will need to explore it yourself.