I am trying to use Montserrat web font (thanks Kathrinvdm!) on my blog. I noticed that the headlines look very different when I open the blog in different browsers. I tried Safari, Chrome and Firefox on my iMac. The font appears much bolder in Firefox. What am I doing wrong?

We would need a link and/or a code sample.

By the sound of it, it looks like FF is applying artificial emboldening instead or in addition to picking the right weight.

Yes, a link or screenshot would help. 

If it’s what Riccardo said and you just call one webfont without a properly linked family, try setting the font-weight this way:

h1, h2, h3, h4, h5, h6 {
    font-weight:normal;
    }

Otherwise, if the fonts just appear slightly different, you probably see the different render engines at play. 

For OS X you can influence this a little bit through:

-webkit-font-smoothing
-moz-osx-font-smoothing

Here is a demo with the possible values for Safari/Chrome: http://files.christophzillgens.com/webkit-font-smoothing.html
For Firefox you can switch to greyscale for lighter text. http://ss64.com/css/font-smoothing.html

 

For OS X you can influence this a little bit through:

-webkit-font-smoothing
-moz-osx-font-smoothing

​Thank you. That helped!