One option that you have is to use sandboxing to prevent that successful attacks reach the underlying operating system. You may be able to mitigate some of those with proper security software. Mozilla patches security vulnerabilities that are found in the browser regularly, which may mean that you are running a version of the browser that is vulnerable to certain attack forms. Running an older version of Firefox may put your system at risk. You can select to install the update, or block it for the time being (for instance to wait for the next release to try again). Instead of installing updates to the browser automatically, Firefox will now display a prompt to you that puts you in control of the update process.

Switch 'Automatically install updates' to 'Check for updates, but let me choose whether to install them'.

Switch to Advanced > Update in the new window.

Tap on the Alt-key and select Tools > Options from the menu bar that opens up.

To block updates in Firefox, do the following:

You may want to disable the automatic updating of the browser for the time being, as you may end up with the same issue after it has been updated. There are however a couple of best practices that I'd recommend you follow before you roll back an update of the browser. Restoring an older version of Firefox is actually not that difficult at all. I ran it from time to time to check for updates, and the latest update today resolved the issue. The core benefit for me was that I could simply switch to Aurora without touching the Nightly version at all. I decided to use Firefox Aurora in the meantime, but the second option would have worked as well. It did not, which left me with two options: use a different channel of Firefox in the meantime or go back to the Nightly version that worked just fine. I was not too worried about that at the time as I knew that Nightly versions of the browser sometimes had hiccups like this, and that the next update would likely fix the issue again. I got weird black bars on the screen that would move around on mouse movement and made it impossible to work with the browser at all. My Firefox Nightly version that I have been running for some time now received an update two days ago that rendered it completely unusable.

Firefox revert to previous version