Does firefox throttle JS or video playback when not focused?
I frequently leave Firefox open with a video stream from twitch.tv full-screened on a second monitor while doing other things (playing games, text editing, etc). If I leave Firefox untouched for long enough (more than a couple minutes, less than an hour) playback will start to stutter or lag (usually video first, eventually audio as well). Clicking Firefox or alt-tabbing very frequently fixes the issue, playback immediately becomes smooth. This is not a recent change, I've observed this behavior for months and finally decided to ask about it.
I have no proof that this is a browser issue. It could be a site-specific issue, (I see it most often on twitch but I have also seen it on other video sites like youtube), an OS issue, or something else.
That said, I could easily imagine it being an intentional browser feature - if Firefox is not focused, throttle JS execution and other resources to save power. In many cases this could be phrased as a feature for the user. Does such a feature, and is it configurable? I've looked through about:config and done some googling and find no mention, but I'm asking here to make sure.
Windows 10 Pro x64 - Firefox 65.0.2 x64
- User Agent: Mozilla/5.0 (Windows NT 10.0; Win64; x64; rv:65.0) Gecko/20100101 Firefox/65.0
So unless another can go to the same site with the same Browser version and replicate the issue that will be hard to know it is a Browser, Memory Buffer, or site or ISP issue.
In Firefox 61, there was a default setting to throttle bandwidth usage in tabs other than the active tab. I think that setting was changed to not do that, but you could check yours:
Throttling is not enabled, and it sounds like this hypothesized feature probably doesn't exist. Thanks for your help, this can be closed.
Would background tab throttling not be a feature of great interest to many users (especially for laptops on battery)? It should also be relatively easy to implement.
I think chrome and opera have it, too. they can throttle background tabs down to 1% of the CPU.
Is this on the development roadmap?
Hi ivo.welch, the original feature throttled bandwidth usage by background tabs, but didn't necessarily reduce CPU usage.
Support forum volunteers aren't always familiar with the details of the development roadmap. If you can't find any useful information in web searches, another place to ask would be the Firefox Development forum: