Failing to add attention in Firefox

[ThomasGreiner]

Environment

• Flattr version: 0.7.0alpha
• Browser name and version: Firefox 66
• OS name and version: Ubuntu 18.10

Steps to reproduce

1. Install extension.
2. Go to any site.
3. Click somewhere.

Observed behavior

• Warning messages are shown in JavaScript console.
• Attention bar in popup does not progress.

Expected behavior

• No warning messages shown in JavaScript console.
• Attention bar in popup progresses.

Warnings

Unhandled rejection: Transaction/<@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:3007:63
nativeAwaitCompatibleWrap/<@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:1532:23
callListener@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:1221:19
endMicroTickScope@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:1302:25
physicalTick@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:1277:30
index.js:1573:25
Unhandled rejection: addAttention/</</<@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:53674:28
callNext@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:4382:56
step/<@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:4385:24
nativeAwaitCompatibleWrap/<@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:1532:23
callListener@moz-extension://7183b64b-4658-4898-82ab-dd28c5f9bb75/lib/background/index.js:1215:19

[erikvold]

I'm thinking #15 might help with this.