Regression: link to create a random mask disappears after pressing the button to create a custom mask and going back

[cadeyrn]

STR:

1. press the blue button to create a custom mask
2. press the back button

Actual:

The link to create a custom mask is no longer there.

Expected:

The link should still be there.

It's a regression since version 2.7.1 of the Firefox add-on.

[cadeyrn]

/cc @maxxcrawford

Thank you for fixing all the reported issues with version 2.7.1! Maybe you could also have a look at this one? It's a regression from one of your changes. Thank you!