Make sure you are not blocking content.

Start Firefox in Safe Mode {web link} by holding down the <Shift> (Mac=Options) key, and then starting Firefox.

A small dialog should appear. Click Start In Safe Mode (not Refresh). Is the problem still there?

One issue that seems more common lately is Firefox's Tracking Protection feature. When it is blocking content in a page, a shield icon will appear at the left end of the address bar next to the padlock icon. This article has more info on managing this feature: Tracking Protection {web link}

I opened Firefox in Safe Mode and was able to login to one of the several sites that I previously was having issues with. I am aware of the Tracking Protection shield but it semed that it does not appear when blocking content. I click on the exclamation point in any case to attempt to have it entered into the exception page but I have issues with this process.

I have read the information on how to disable protection but am still have issues.

Apparently something is being blocked so the shield does not appear and give me the option to disable.

Hope this helps. Still having issues with other site logins.

Start your Computer in safe mode with network support. Then start Firefox. Try Secure websites. Is the problem still there?

http://encyclopedia2.thefreedictionary.com/Linux+Safe+Mode Starting Any Computer In Safe Mode; Free Online Encyclopedia

Sorry for delay in response. Still having issues. Finding that some of the windows (allow Adobe flash etc) are not appearing. This is only one problem. I fail to see the shield appear in site address bar so I can choose whether or not to disable tracking etc.

Still locks up on occasion so find that I force a shutdown, open Firefox in safe mode, clean cache and then try again in normal boot mode. Seems then to work with site previously causing lock up.

Working on it but just strange.

ramtuf

Are you saying there is no problem in Safe Mode?

It could be the work of one of your add-ons, or it could be Hardware Acceleration. How to disable Hardware Acceleration {web link}

Type about:addons<enter> in the address bar to open your Add-ons Manager. Hot key; <Control> (Mac=<Command>) <Shift> A)

In the Add-ons Manager, on the left, select Extensions. Disable a few add-ons, then Restart Firefox.

Some added toolbar and anti-virus add-ons are known to cause Firefox issues. Disable All Of them.

If the problem continues, disable some more (restarting FF). Continue until the problem is gone. After, you know what group is causing the issue. Re-enable the last group ONE AT A TIME (restarting FF) until the problem returns.

Once you think you found the problem, disable that and re-enable all the others, then restart again. Let us know who the suspect is, detective.