Press Help and select Restart with Add-ons Disabled..., then check if this is happening also in the Safe Mode.

When you say it locks up, what happens? Do you get NOT RESPONDING in the title bar, or the page just never finishes loading, or an unresponsive script warning dialog, or ??

Thank you for sharing your extensions list. This one looks questionable based on reviews:

SearchLock - https://addons.mozilla.org/firefox/addon/searchlock/

You can view, disable, and often remove unwanted or unknown extensions on the Add-ons page. Either:

• Ctrl+Shift+a (Mac: Command+Shift+a)
• "3-bar" menu button (or Tools menu) > Add-ons

In the left column, click Extensions. Then cast a critical eye over the list on the right side. All Mozilla-installed extensions are hidden from this page, so what you see listed here is your choice (and your responsibility) to enable, disable, or remove. If in doubt, disable.

Often a link will appear above at least one disabled extension to restart Firefox. You can complete your work on the tab and click one of the links as the last step.

Any improvement?