Since updating to 40.0 my upload speeds have dropped although download speeds are the same. Why?
Since Firefox has updated to 40.0 on my iMac running 10.9.5 I have noticed that whilst my download speeds have remained constant at approx 68 Mbps my upload speeds have dropped from 16 Mbps to 14 Mbps. The same change IS NOT occurring when using Chrome or Safari so I surmise that Firefox is the problem. The problem is consistently evidenced when testing speeds with some speedtesters eg BT Wholesale and Mybroadbandspeed.co.uk but not with Speedtest.net which reports my usual speeds.
Krejt Përgjigjet (4)
Hello,
Some anti-virus or firewall programs specifically targeting Firefox may cause this. There may also be add-ons interfering with your results.
Try Firefox Safe Mode to see if the problem goes away. Firefox Safe Mode is a troubleshooting mode that temporarily turns off hardware acceleration, resets some settings, and disables add-ons (extensions and themes).
If Firefox is open, you can restart in Firefox Safe Mode from the Help menu:
- Click the menu button
, click Help 
and select Restart with Add-ons Disabled.
If Firefox is not running, you can start Firefox in Safe Mode as follows:
- On Windows: Hold the Shift key when you open the Firefox desktop or Start menu shortcut.
- On Mac: Hold the option key while starting Firefox.
- On Linux: Quit Firefox, go to your Terminal and run firefox -safe-mode
(you may need to specify the Firefox installation path e.g. /usr/lib/firefox)
When the Firefox Safe Mode window appears, select "Start in Safe Mode".
If the issue is not present in Firefox Safe Mode, your problem is probably caused by an extension, theme, or hardware acceleration. Please follow the steps in the Troubleshoot extensions, themes and hardware acceleration issues to solve common Firefox problems article to find the cause.
To exit Firefox Safe Mode, just close Firefox and wait a few seconds before opening Firefox for normal use again.
When you figure out what's causing your issues, please let us know. It might help others with the same problem.
Hi Andrew,
I have tried all the suggestions that you have made but none of them make any difference.
When using Firefox BT Wholesale Speedtester and Mybroadbandspeed.co.uk consistently report my Upload speed as 2 MBps lower than the same testers do when using Safari or Chrome as my browser. Download speed reports do not seem to be affected, any small differences shown being explained by the general minor variations in speed that one always sees as speeds vary a little and reports are just a "snapshot in time".
This was NOT the case before updating to Firefox 40.0 so logically it would appear that something in the update has caused the difference.
Anyone got any more suggestions?
Most testing sites use the Shockwave Flash plugin, so issues with this plugin will affect the results.
You try the test with HTML5 to see if that produces different results.
Hi Cor-el
The point I have been making (the query I have posed) is why, after updating to Firefox 40.0 from the previous release have the reported upload speeds dropped when using 2 specific spreed test sites when they haven't dropped when using using different browsers to test using the same sites? If the problem is with the Shockwave Flash Plugin then surely it would replicate the same results irrespective of which browser is being used to utilise the plugin to run the test?
Of course I can always use a different browser to run the test. However, in the past all the bowsers I used produced the same results (within experimental error) when utilising the same test site - now they don't.
So helpful though your idea is to use a test site utilising HTML5 in order to get a result it doesn't, unfortunately, address my query.