[Firefox <=57] Incompatible with script produced by Webpack + Babel + core-js2

[machsix]

Expected Behavior

Script runs normally like Chrome 48+Tampermonkey and produces the following content in the console

Actual Behavior

An error is generated for Firefox 52 ESR or Firefox 57 with Tampermonkey

The error is not reproducible in

• Firefox 52 ESR or Firefox 57 with Violentmonkey
• Firefox 68 ESR with Tampermonkey
• When bundle the script with core-js@2 but not core-js@3

Specifications

• Firefox 52 ESR (downloaded from https://portableapps.com/apps/internet/firefox-portable-legacy-52), Firefox 57
• TM: 4.9.6095
• OS: Windows 10

Script

The script is generated with Webpack + @babel/plugin-transform-runtime + @babel/runtime-corejs3. If I use Webpack + @babel/plugin-transform-runtime + @babel/runtime-corejs2, everything works normally. I hosted the minimum example at

• core-js@3: https://github.com/machsix/tampermonkey_bug
• core-js@2: https://github.com/machsix/tampermonkey_bug/tree/core-js%402

Entry point is /src/index.js

The produced userscript is at /dist/test.user.js

[derjanb]

Well that's a Firefox issue. Somehow the FF folks thought it would be a good idea to have global properties which are not part of the global object.

Symbol is one of these in FF 52. That's why Tampermonkey misses this property.

You can workaround the issue by either adding

// @grant none

to your script or by adding

window.Symbol = Symbol;

as first line after the header.