What would be an example of something you want to forward?

Many sites have a "share" feature built-in that lets you email a link, or copy something to your social networking feeds, etc.

If the site doesn't have a built-in feature, some platforms offer you a universal button (e.g., the Pin It button from Pinterest) that you can store on your Bookmarks Toolbar to grab content from a page.

If you can be more specific, so can we. :-)

Here's an example. I get an email from a source that contains several news articles. Using Firefox, I open one of these articles, and would like to forward it to a friend using my Gmail address book. There is no "Forward" link that I can find.

I think the easiest way would be to forward the message you received and edit out the parts you do not want to forward.

When you're viewing an individual attachment, your options would depend on whether it's a web page, a PDF, an image, etc. I don't think there's a universal button for "attach what I'm viewing to a Gmail message." Unless someone created an add-on for that...