Questions on backwards compatibility of Firefox Addons/Extensions

Question

Background info:

Over the past week, I have been messing around with Chrome extensions and had no problem creating my extension. Great, Chrome rocks for making the development process very easy to learn, and, well... just easy!

Now I have it in my mind that I'd like to create this extension for as many browsers as I can, so I decided on Firefox next.

What a mess! There documentation has done nothing but give me a headache and waste my time so far, VERY convoluted and just generally unorganized.

I have managed to locate a code sample for a simple extension that I think I can use as a starting point and have begun messing around with - fine...

I have learned that this sample extension will not work with anything less than Firefox 4, as it uses the bootstrap technique to make the extension installable without a browser restart. Ughhhhhh....

Now we arrive at my questions:

1. Is it possible to develop an extension for Firefox 7 that will work with previous versions of Firefox? I don't even care about anything prior to Firefox 4, if that's the cutoff point for restart-less installations. It would be nice to know that what I am spending all this time making will work consistently and for more than a week when the user is prompted to upgrade next.

2. How about the reverse? Can I create an extension that is compatible with Firefox 3.5 through Firefox 7? I realize it would require a restart to install, but that would be acceptable if it resulted in a working extension regardless of the version.

3. Can anyone with experience on this stuff share a bit of what I'm getting myself into here? It seems like this is a nightmare of a platform to develop on, and that I will be constantly fixing my extension.

One last piece of relevant information:

The extension I am developing is purely javascript based - this stuff should work (I think?) because it's dependent on just one feature "content scripts" that really shouldn't be changing in implementation between versions at this point... right?

So what exactly am I missing? How do you create easily manageable Firefox extensions that will work in all versions of the browser?

Thanks everyone! :)

Answer 1

You have to distinguish between "traditional" extensions and extensions built with the Add-on SDK. The former are far more powerful given that they have direct access to all APIs the browser uses - but that's also the reason why they are more complicated to write and why the documentation is rather unordered (there are simply very many things that you could do, far more than you could with Chrome). They are also more likely to break as the browser changes. The Add-on SDK on the other hand gives you a limited API much like Chrome. The Add-on SDK currently supports everything from Firefox 4 onwards (yes, because of restartless installation), with the promise that browser changes will merely require your add-on to be recompiled with a newer version of the Add-on SDK. In fact, that recompiling will likely happen automatically in future for add-ons hosted on addons.mozilla.org. On to your questions:

Is it possible to develop an extension for Firefox 7 that will work with previous versions of Firefox?

Sure it is. The Add-on SDK currently marks your add-on as compatible with anything between Firefox 4 Beta 7 and Firefox 8 Alpha 1. Even as traditional add-ons go - starting with Firefox 4 the differences between particular browser versions are rather small, most things work in all of them. You can also stay compatible with Firefox 3.x but depending on what you do it might require some effort. Important information:

• Firefox 4 for developers
• Firefox 5 for developers
• Firefox 6 for developers
• Firefox 7 for developers

How about the reverse? Can I create an extension that is compatible with Firefox 3.5 through Firefox 7?

It doesn't matter which way you go. I wouldn't recommend spending much time on Firefox 3.x support however. With Firefox 3.5 no longer supported the only relevant version is Firefox 3.6. According to the statistics of my add-ons roughly 18% of the Firefox users continue using it. In the next few months this percentage will get significantly smaller, especially when Mozilla announces end-of-life for this branch. So for a new add-on supporting it is usually not justified.

Can anyone with experience on this stuff share a bit of what I'm getting myself into here?

Depends on how complicated your add-on will be. Given that you are developing an equivalent to a Chrome extension, you will most likely be using the Add-on SDK which means that there won't be any compatibility problems. As traditional add-ons go, simple add-ons that don't rely on some obscure implementation details also typically don't have any trouble staying compatible (I have two add-ons that didn't need a single adjustment since Firefox 3.5). Add-ons that go deep down into the system are more problematic of course.