Inline styles do ot work in issue editor with Firefox
Summary
Inline formatting via issue editor buttons (for example bolding and italic) disappear when saving the issue description or comment in Firefox on Windows.
Steps to reproduce
Write some text to issue description or comment box, then select it, press bold and/or italic button and save issue. The stars disappear around the text and bold/italic text isn't shown. Happens in Firefox browser, at least in Chrome this works normally. In preview prior the saving, the styles are shown correctly. OS: Windows 10 64-bit Firefox versions 54.0.1 32-bit & 55.0 64-bit Chrome version 60.0.3112.90 64-bit
Example Project
https://gitlab.com/hannu.viidakko/sandbox/issues/1 or this issue.
What is the current bug behavior?
Bold and/or italic formatting disappears.
What is the expected correct behavior?
Bolded and/or italic text.
Relevant logs and/or screenshots
Output of checks
Results of GitLab environment info
Happens in gitlab.com as well as in our GitLab Enterprise Edition 9.4.3-ee 9f45c320 installed via Omnibus package to Debian Jessie platform (got no sudos to installation, so can't paste the details).