What you think about speed testing of your internet connection ? Run a scan with www.speedtest.net/ and see the ongoing speed . if it is good enough then try Down Them All ,it will gives you capability to download all images and media(only those which are signed for freeware download) as well as accelerate speed. One more is speed-tweaks add-ons ,which gives you central settings control with best fit values.

However if you want to Refresh Firefox then it also performs a factory settings for firefox . But be aware about this because it may alter your settings as well as bookmarks and passwords too .

"How can I test my download and upload speeds?" http://support.brighthouse.com/Article/Test-Download-And-Upload-Speed-1583/ Test page for Bright House Networks.

"Internet accelerators" are made for each specific internet service provider, typically for dial-up or ADSL services to"cache" content [somewhat locally] that as accessed frequently by their customers so that "all" content doesn't always have to load all the way from the originating server for the webpage content. IOW, it provides a shorter "path" for files [particularly images] that are loaded by a lot of customers in the local area.

An external download manager might be useful to you.

Boot the computer in Windows Safe Mode with network support (press F8 on the boot screen) as a test to see if that helps.

• http://www.bleepingcomputer.com/tutorials/how-to-start-windows-in-safe-mode/
• http://www.7tutorials.com/4-ways-boot-safe-mode-windows-10

Start Firefox in Safe Mode to check if one of the extensions (Firefox/Tools > Add-ons > Extensions) or if hardware acceleration is causing the problem.

• Switch to the DEFAULT theme: Firefox/Tools > Add-ons > Appearance
• Do NOT click the Reset button on the Safe Mode start window

• https://support.mozilla.org/kb/Safe+Mode
• https://support.mozilla.org/kb/Troubleshooting+extensions+and+themes