This is specific for Firefox as far as I know. If you have seen a page popping up with the familiar firefox orange with the logo in the middle saying an urgent patch is needed. ( have attached an example screenshot). DO NOT continue. Close the tab.
This does not mean your computer is infected. It is appearing for people typically when they visit sites that have lots of ads. This is often reported from people visiting the big news sites. BBC, CNN, ect. The source is from one or more infected adware sites and something unique in how Firefox works with flash or java allows this.
From a post from Mozilla moderators in their forum, this addon is suggested as something everyone should have. It is an ad blocker that blocks ads from known malware sources and is updated daily. Reviews say it is light on cpu and bandwidth use so should not bog you down. These days, with ads being everywhere, the advice to use a sound ad blocker is as important as having overall security software running.
The addon for firefox is at.https://addons.mozilla.org/en-US/firefox/addon/ublock-origin/
Additionally, it is a good idea to sweep your computer once a month or more with something like the freeware version of Malware Bytes. It will find and delete ordinary things like trackers (You ever wonder why, after you search for cheese that you start seeing ads for cheese on your regular web browsing sites?), which are like mosquitoes, no matter what you do, they still get in.