[webextension] Errors while using Block element in Firefox 51-58

[Ross]

Environment

ABP 3.0.2.1968
Firefox 51 / Firefox 58 / Windows 7

How to reproduce

1. Navigate to a site, such as ​https://en.wikipedia.org/wiki/Main_Page
2. [ABP Icon] > [Block element].
3. Block section of the page or cancel the dialog.

Observed behaviour

Blocking an element, or exiting the blocking state appears to work as expected but several errors still appear in the console.

In Firefox 58:

TypeError: cannot use 'in' operator to search for 'canGoBack' in 'browser'[Learn More] tabbrowser.xml:2485:1
NS_ERROR_NOT_INITIALIZED: Component returned failure code: 0xc1f30001 (NS_ERROR_NOT_INITIALIZED) [nsIMessageSender.sendAsyncMessage] ext-windows.js:19
Ignoring response to aborted listener for 252
Ignoring response to aborted listener for 282
Error: port.onDisconnect.hasListeners is not a function undefined
Error: Message manager disconnected

In Firefox 51:

Error: port.onDisconnect.hasListeners is not a function (unknown)
Error: Could not establish connection. Receiving end does not exist.

Expected behaviour

No errors to occur (if possible).

[kzar]

This is a Firefox bug and apparently fixed in Firefox 60, see ​https://bugzilla.mozilla.org/show_bug.cgi?id=1436351

[greiner]

We still support older versions of Firefox though so is there a way we could work around this bug until we drop support for those?

[kzar]

Well the block element feature still works, it's just an error is displayed in the console. Perhaps there's a way to workaround the error but I can't see one.

[greiner]

If the error is merely cosmetical and doesn't cause any issues, I agree that we can safely ignore it. Thanks for clarifying.