I'm not sure Mac behaves like Windows or Linux (I think so), but this may be a simple issue of Firefox's window suddenly loosing focus. Does it also work if, instead of clicking a link or refreshing the page, you simply click on the window (anywhere that doesn't do anything)? If that's the case, it's a problem with focus, most likely.

I fear I can't be further assistance though. I'm not a Mac user.

Start Firefox in Diagnose Firefox issues using Troubleshoot Mode to check if one of your add-ons is causing your problem (switch to the DEFAULT theme: Tools > Add-ons > Themes).
See Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems and Troubleshoot issues with plugins like Flash or Java to fix common Firefox problems

If it does work in Safe-mode then disable all your extensions and then try to find which is causing it by enabling one at a time until the problem reappears.
You can use "Disable all add-ons" on the Safe mode start window to disable all extensions.
You have to close and restart Firefox after each change via "File > Exit" (Mac: "Firefox > Quit"; Linux: "File > Quit")

Hi cor-el, Thanks for the tip, but I'm afraid that didn't seem to help any. All Add-ons are off, and I still have the same issue.

Morbus - I did try that, as I've experienced similar things before. I'm afraid it doesn't work, though...

Let's keep hoping!