Start Firefox in Safe Mode {web Link} by holding down the <Shift>
(Mac Options) key, and then starting Firefox. Is the problem still there?

FFuser42 said

Typing characters appears seconds later (such as providing these details). Websites are loading slowly.

Thanks, this has resolved the speed and typing issue. I noticed pop up ads have reappeared so I will need to block them. Also, does this mean I have to start FF in safe mode each time I access it?

Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes). If the problem goes away, that tells us one thing. If it does not, that tells us something else.

It could be the work of one of your add-ons. 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.

Just as an update, after investigation of general hardware acceleration issues there is an update going out today that should resolve this. The new version will be 38.0.5 beta June 2*. Thank you for your patience, please do report back if there are any further issues.

(*please note the update in this post for the change in release channel also subject to change)

for fixing this issue, please also refer to: Firefox is slow after updating to Firefox 38

The response from Philipp to uncheck the "Use hardware acceleration" box appears to have fixed the speed and typing issue. However, the ad pop ups have reappeared so I will need to reblock them. Not sure if the long term fix mentioned in the instructions to uncheck the hardware acceleration box is what was noted in the response from guigs2.

From Mozilla help files;

Try disabling graphics hardware acceleration. Since this feature was added to Firefox, it has gradually improved, but there still are a few glitches.

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