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")

Thank you cor-el. Disabled all add-ins. Firefox is now working the way it did before the update.

Easy fix for below error:

"A script on this page may be busy, or it may have stopped responding. You can stop the script now, or you can continue to see if the script will complete.

Script: chrome://tavgp/content/libs/include.js:595"

Tools > Add Ons > Extensions > AVG Security Toolbar (version number)[DISABLE]

You only need to disable the relevant add-on the clue is in the javascript link 'tAVGp' meaning it is to do with either the AVG Toolbar or another AVG add-on so those are the ones you need to disable no need to disable ALL add-ons or to go into safe-mode, try disabling the AVG toolbar add-on first (as other AVG add-ons are likely to be disabled for being out of date anyway).

You do not need to disable it in safe mode I didn't and it now works fine after disabling that one add-on.

So to recap: Tools > Add Ons > Extensions > AVG Security Toolbar [DISABLE]

JOB DONE!

This will save you doing each one indiviually to see which one it is, however if you are not using AVG for anti-virus then you will need to disable all of them.

Anybody get this who DOESN'T have AVG on their system? That would be interesting.

You only get this specific error if you have the offending AG extension identified as tavgp.

You can see this script (if the extension is enabled) if you paste the chrome URL in the location bar and pres Enter or click the Go button.

• chrome://tavgp/content/libs/include.js