I've had this problem with HTTPS Everywhere 4 on laptop for some time. Basically if the extension is active Firefox will partially load and then peg one of the CPU cores. Today I decided to uninstall/reinstall Firefox, but that didn't fix the problem. The laptop runs Windows 7x86. I have HTTPS Everywhere working fine on my desktop/Windows 7x64. I have Sync enabled in Firefox so apart from HTTPS Everywhere the two installs use the same extensions and plugins. Thanks for any suggestions.
HTTPS Everywhere 4 is working fine on my 3 computers (desktop, 2 laptops), with all 3 of my browsers and never had a problem with it.
I won't be surprised if the cause of the problem is elsewhere. I'm going to disable all of the extensions and then reinstall HTTPS Everywhere. If Firefox starts OK with just HTTPS Everywhere I'll enable the other extensions one at a time and see if I can isolate the problem.
Like others are saying, disable all your addons to see if it's just HTTPS Everywhere 4. If it is a legit bug, you can downgrade to a version that works and report your issue either here: https://github.com/EFForg/https-everywhere or here: https://trac.torproject.org/projects/tor/report/19
I was able to solve the problem by disabling all of the security add-ons, installing HTTPS Everywhere 4 (which then worked fine) and re-enabling the add-ons one at a time. It turned out to be a conflict between HTTPS Everywhere and Calomel SSL Validation. These two add-ons get along fine on my desktop PC, but for some reason don't on the laptop. I'll leave Calomel SSL disabled for now and revisit the issue when one or the other add-on is updated. Thanks to everyone who responded.
