I notice this every time I upload anything on Firefox as the laptop fans get really loud. Checking task manager, FF is using approximately 20% of the CPU and the only thing it is doing is uploading. Playing a 4K YouTube video in addition to this in FF only adds an extra 10%. That's 4K video, why is uploading at a very low bitrate requiring double the CPU resources? The laptop I'm using is designed to edit videos while rendering effects onto them in realtime, this is the only reason I've noticed this as Firefox is noticeably more taxing on average with uploads then when I'm editing videos. Here's a thread that also mentions the same problem but on lower spec machines it seems like FF is using almost 100% of the CPU, yikes! https://support.mozilla.org/en-US/questions/1018059 It seems to me that FF version 32 and above have this issue. I'll try version 31 after the upload is done to see if it works fine. Let me know if you require additional information?