[x] Correctly handle not yet supported “visible” property for browser.contextMenus.create() in Firefox 60 – 62, context menu for selected text links will actually work only in Firefox 63+.

[x] Correctly stop wait for browser.webRequest.onSendHeaders in case of blocked request.
[+] Added support for selected text links (Firefox 60+).

[*] Updated hotkey validation: mark as invalid only if browser.commands.update() failed.
[+] Added ability to close tab/window using Esc key.
[x] Workaround to show request headers in case of browser.webRequest.onSendHeaders notification after server response.

Ported to WebExpensions.
Changelog: https://github.com/Infocatcher/Link_Properties_Plus_WE/blob/master/changelog.md