Ok, this is a very simple one, yet, I am very curious about it.
Recently I discovered that in some modern (and very well done) design themes developers renounce declaring -moz- and -o- (ok forget about -ms- anyhow) for CSS transforms. So that instead of i.g. having:
-webkit-transition: -webkit-transform 0.315s ease-in-out;
-moz-transition: -webkit-transform 0.315s ease-in-out;
-o-transition: -webkit-transform 0.315s ease-in-out;
transition: transform 0.315s ease-in-out;
they simply use:
-webkit-transition: -webkit-transform 0.315s ease-in-out;
transition: transform 0.315s ease-in-out;
Is there a good reason for this or do they simple not care about other browsers? Is it maybe because also modern Firefox or Opera browser do work with transition without prefix?
I would also love to implement the lighter version 2 in my designs but I am not sure about that. Any explanations from the pros here?
Depends on what browsers and what versions they are aiming for. To the extent of my Webkit experience is that Webkit will likely almost always fall back on the -webkit annotation if the standardized rule fails to parse. I have written quite a few front-ends and I have not seen the newer versions of Firefox use the moz annotation, except when it was quite a new feature like object-fit or filters.
Small word of advice: if you're running Gulp or Grunt, I would advice using CSS-autoprefixer. This plugin does the prefixing for you.