fix: use getRoot request to support Firefox 77+

[Rob--W]

Fixes #1884.

• Firefox 77+ requires getRoot because listTabs was removed in https://bugzilla.mozilla.org/show_bug.cgi?id=1618691
• getRoot is supported since Firefox 55, with https://bugzilla.mozilla.org/show_bug.cgi?id=1352157
• I still added a getList fallback to not unnecessarily breaking backwards compatibility, so this is a safe patch for a minor release.

[coveralls]

Coverage remained the same at 100.0% when pulling 5e89238 on Rob--W:firefox-remote-77-listTabs-to-getRoot into e0d4c3c on mozilla:master.

[willdurand]

ha well, I was also working on that issue.. I guess I can move on something else now :)

[rpl]

👍 lgtm, just a couple of small optional nits.

[rpl]

ha well, I was also working on that issue.. I guess I can move on something else now :)

ouch, I'm so sorry @willdurand. I'm the one to blame, there was an assigned comment in our shared triaging meeting document but (to make sure that it couldn't be missed) I should have explicitly assigned you the issue and added a comment to mention that you were going to prepare a pull request for it by today or tomorrow.

[0c0w3]

Can this be merged soon? It's making it hard for me to develop an add-on against an m-c build with patches applied. (I'm on the urlbar team and I'm developing a urlbar WebExtensions API.)

[rehandalal]

Can this be merged soon?

+1 - it's interfering with our work on the experiments infrastructure team as well.

[rpl]

Can this be merged soon? It's making it hard for me to develop an add-on against an m-c build with patches applied. (I'm on the urlbar team and I'm developing a urlbar WebExtensions API.)

@0c0w3 @rehandalal sure, I plan to merge this today and we should also be able to release it on npm as well.

[0c0w3]

Thanks! (Thanks for web-ext too, it's nice.)

[rpl]

@0c0w3 @rehandalal this has been just released on npm as v4.2.0 (See release notes to know which other changes are included in the new version along with this fix).

Let us know if any other issue in the newly released version is still blocking you.

[rehandalal]

@rpl thanks for the release! it's working great for me on Ubuntu but my teammate is having an unrelated issue with this release and Nightly on MacOS that is a complete blocker.