Opening new child/sibling places unwanted text in the address bar

[TempSpas]

With the update to version 1.5.1, the added feature that places focus on the address bar when opening a new child/sibling tab has the unintended consequence of populating the entry field with the character from the keyboard shortcut. Steps to reproduce:

1. Open a child or sibling via the keyboard shortcut Option+Shift+O or Option+Shift+I.
2. Observe that in the former case, the Ø character populates the entry field. In the latter case, the ˆ character populates the field.

This is on Firefox 55.0.1, macOS 10.12.6.

[mrphang]

I just tried it on FF 56.0 on Linux Mint and was unable to reproduce.

[TempSpas]

Perhaps it's specific to macOS then. I'm on Firefox 56 and macOS 10.13 and the issue persists. Attached is a gif of the bug in action.