Viewport width broken by long url-like strings that don't wrap

This is a follow up to issue 2642592 → .

I'm having similar issues with header width on pages where the Add new comment form is displayed.

But I now think this has nothing to do with the Comment form (see fix in related issue → ) because the width of the header varies quite a bit from page to page (articles where comments are enabled).

The varying header's width appears to be dependent on long strings i.e. URLs that do not wrap properly. Here are a few examples.

1. /admin/config/regional/translate/translate
2. /admin/commerce/config/payment-methods/manage/commerce_payment_commerce_stripe)
3. /sites/all/themes/mytheme/js/toggler.js

Any ideas how to solve this?