Please consider turning on send info to Mozilla from with in Firefox before posting a question. This helps us help you. I have no info from your system that would help see things that cause issues. I can not see anything to help answer that question.

Find Extensions that stop videos from pre-loading : https://addons.mozilla.org/en-US/firefox/extensions/ Such as CNN it loads the video even of do not watch it. is one way. Stop ads from loading, use adblockers (do not know if have as can not see any). Stop going to youtube, select lower quality videos like 420p. Keep system and firefox clean. https://www.howtogeek.com/

Check for any bitcoin miners or other things that have got in. Please use more than 1 scanner as each uses diff tech :

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware

Save your Report and google each before deleting anything as do not want to delete something you need, If need help :

• https://forums.malwarebytes.com/topic/9573-im-infected-what-do-i-do-now/

Post in only 1 forum, then wait.

Please let us know if this solved your issue or if need further assistance.

Cool, sorry about that, bit of a neophyte. I have the boxes marked within firefox to send info to Mozilla. Not sure which system information you might need or how it was supposed to load with the question. Let me know what information I can add in here that would prove helpful. Or if re-asking the question would be better.

As far as extensions the only two I have on Firefox are Disable Autoplay 5 and Honey. That's it.

Can't remember the last time I went to YouTube on this machine.

Currently running malwarebytes and bitdefender to see if anything pops up there.

Comcast said 700 GB of data was used on 3/19/18 alone. 130GB of data was used on 3/18/18. Clearly there was some sort of spike.

Ya no, just if next time post turn it on please as sends us your version info, flash ver, add-ons, video card drivers and error messages in them. That's it, nothing more.

You could check by copy/paste Event Viewer into search then run it. Then go through the logs for that day and see what was going on.

You can also do : History Short Cut; <Control><Shift> H and view your Browsing History/downloads to, no dates though.

Did windows update to another version on that date ? Can view in Settings --> Update & Security --> View Installed Update History and google the KB# for size if it matches your date. There was a large one just recently. Also can change your Download in Advanced, 2x's and change how much gets downloaded.

There are many things on a computer that uses the net. Adds, Pictures, Music . . . .

Also, many programs 'Phone Home.' Disable this in all programs, but remember to manually check now and then. This includes Firefox and its add-ons.

Go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) and search for a good ad / pop-up blocker.

The Firefox web browser itself may have used very little bandwidth.

There is a long list of things that use a lot of bandwidth data in a month.

Streaming video and audio (whether on PC, Tv, game consoles, media player, or Blu-ray players that can do streaming) from Youtube, Netflix, Pandora, online Tv channel sites, and the like etc can add up on bandwidth use very easily, especially if at higher quality options like 1080p and up more so with 4K.

Game download (and updates even) on consoles and Steam can be large to very large sometimes. Whether 1GB to almost 48GB for Sony PS4 though I swear I saw a recent game needing 85GB and up to 116.77GB for Xbox One. Online gaming and chatting can use a lot of bandwidth.

Peer to Peer Applications for file sharing and BitTorrent for example can use a lot.

Computers infected with Malware (more likely to occur on Windows vs Mac or Linux) can leave your computer vulnerable to many forms of abuse. Can be used as part of a Botnet, for spam or as a server for something for examples.

OS updates and software download/updates can use a lot of data.

Wifi being used by unauthorized people. Not everybody changes the default username and password for their router and or sets up a solid custom password for wifi access. I remember a group of people in my Province over ten years ago worked together driving around over time seeing how many wifi routers they could detect and access with the common default username/passwords used by the brands and models available up to that time. They made a map of it in their attempt to make people be aware as far too many people never bothered to change from the default.

FredMcD said

Go to the Mozilla Add-ons Web Page {web Link} (There’s a lot of good stuff here) and search for a good ad / pop-up blocker.

The web browser we know as Firefox has had a built-in popup blocker since forever as I think you meant to look for extensions that can add features to the popup blocker.

Are you possibly using Sync?

See also:

• https://support.mozilla.org/en-US/kb/troubleshoot-firefox-issues-caused-malware