Is this when you open the browser, or is the browser already open?

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?

https://support.mozilla.org/kb/Firefox+is+already+running+but+is+not+responding

https://support.mozilla.org/en-US/kb/firefox-slow-how-make-it-faster

https://support.mozilla.org/en-US/kb/firefox-uses-too-many-cpu-resources-how-fix

https://support.mozilla.org/en-US/kb/firefox-uses-too-much-memory-ram

https://support.mozilla.org/en-US/kb/firefox-hangs-or-not-responding

It starts after the browser is already open and I hit a bookmark to go to another website, it takes forever to fully open the page. If I use another browser my speeds are fine and all the different websites open as usual.

The problem started on Thursday when Firefox automatically updated to version 60.0.1, no problems before the update.

Hi, you can try these : Please go to Options --> General --> Performance and uncheck the box for Use Recommended Settings and try changing the Process count to 2 and can also go up but note more cpu and ram will be used. You will need to reboot after makng any changes.

Then go to Privacy & Security and down to Permissions. Please ensure that the box for Prevent Accessibility Services from accessing your browser is checked.

It is possible that your firewall or other security software blocks or restricts Firefox without informing you, possibly after detecting changes (update) to the Firefox application. Remove all rules for Firefox from the permissions list in the firewall and let your firewall ask again for permission to get full, unrestricted, access for Firefox and the plugin-container process and the updater process. See:

• https://support.mozilla.org/en-US/kb/server-not-found-connection-problem
• https://support.mozilla.org/en-US/kb/Firewalls
• https://support.mozilla.org/en-US/kb/fix-problems-connecting-websites-after-updating