alert, confirm and prompt methods don't work on Firefox

[xuhcc]

Describe the bug

It seems that on Firefox, alert(), confirm() and prompt() are not allowed in background scripts:

• alert method executes successfully, but it doesn't show any dialog boxes. These messages are printed to the browser console:

alert() is not supported in background windows; please use console.log instead.        background.js:1:47278
MetaMask Notice:
http://localhost:8081/package.json States:
Hello, localhost!        background.js:1:47278

• confirm and prompt methods fail with this error:

TypeError: window.gBrowser is undefined        PromptParent.jsm:182:21

To Reproduce

Execute wallet.send({ method: 'prompt', params: ['test'] }); from a plugin module.

Expected behavior

I expected these methods to show dialog boxes.

Browser details (please complete the following information):

• OS: Linux
• Browser: Firefox 70.0.1
• MetaMask Version: AddIdentityApi branch

[rekmarks]

@xuhcc, thank you for bringing this to our attention. We have plans to add a more comprehensive notification API that will be compatible with all browsers. This will unfortunately have to wait until we get around to that.

In related news, we've decided to make Google Chrome (and by extension, probably up-to-date Chromium browsers as well) the only officially supported browser for beta at this time. We will fully support Firefox as we approach the launch date sometime in 2020.