When attempting to run a second web-ext process that uses the same browser profile, there should be a way to tell the user that profile is locked, or it can't be used.

[tommai78101]

Is this a feature request or a bug?

Feature request

What is the current behavior?

The current behavior shows when you attempt to run web-ext twice or multiple times, the second web-ext process would do the following in order:

1. Outputs a message stating to "Use --verbose or open...".
2. Runs the browser of choice.
3. Immediately closes/shutdowns the browser.
4. Throw exception and outputs to the terminal with the following message:

WebExtError: Temporary add-on installation is not supported in this version of Firefox (you need Firefox 49 or higher). For older Firefox versions, use --pre-install
at FirefoxDesktopExtensionRunner._callee6$ (C:\Users\user\AppData\Roaming\npm\node_modules\web-ext\dist\webpack:\src\extension-runners\firefox-desktop.js:273:19)
at tryCatch (C:\Users\user\AppData\Roaming\npm\node_modules\web-ext\node_modules\regenerator-runtime\runtime.js:62:40)
at Generator.invoke [as _invoke] (C:\Users\user\AppData\Roaming\npm\node_modules\web-ext\node_modules\regenerator-runtime\runtime.js:296:22)
at Generator.prototype.(anonymous function) [as throw] (C:\Users\user\AppData\Roaming\npm\node_modules\web-ext\node_modules\regenerator-runtime\runtime.js:114:21)
at step (C:\Users\user\AppData\Roaming\npm\node_modules\web-ext\dist\webpack:\node_modules\babel-runtime\helpers\asyncToGenerator.js:17:1)
at C:\Users\user\AppData\Roaming\npm\node_modules\web-ext\dist\webpack:\node_modules\babel-runtime\helpers\asyncToGenerator.js:30:1
at process._tickCallback (internal/process/next_tick.js:103:7)

What is the expected or desired behavior?

There should be an error message stating that web-ext cannot run because another web-ext is using the given browser profile. And not stating that the temporary add-on installation not being supported for Firefox 49 or higher.

I am using Firefox Dev Edition v60 beta 2, so this error message is misleading at best.