Issue / merge request filter layout responsiveness broken on Firefox since GitLab v11.11

This issue is found since GitLab v11.11

Below are screenshots of https://gitlab.com/gitlab-org/gitlab-ce/issues

When the zoom level is not 100%, the layout of the filter bar is (easily) broken on Firefox (may still depends on the font family and size): image

(Tested on v67.0 (64-bit) on Windows 10, macOS v10.14.4 & Linux Mint v19.1 Tessa)

However it's totally fine on Google Chrome, even the display zoom level is 250% image

As it worked well before, I think it might be a bug which worth a issue report 😃

Let me know what else information should I provide if it's missing, thank you all for making GitLab awesome!