I added Fira Sans to my Webflow projects via the 'Choose from font list' part of the Fonts settings and I'm seeing issues in IE.
It seems there is a semi-known issue with Fira Sans where its baseline appears significantly higher on IE (and it looks a little high to me in FF and Chrome as well).
Example: Notice the vertical alignment of the button text.
I wanted to point this out to the WF team, and see if anyone else gets this with Fira Sans. Thanks!