Waterfox Classic: e10s: multiple processes (one content process) in single-process mode

[grahamperrin]

Observable with:

• Waterfox Classic 2019.10 (20191103135811) on FreeBSD-CURRENT
• Waterfox Classic 2019.10 (20191023220600) on Manjaro Linux.

On Linux, the unexpected content process seems to be triggered by some types of new tab action:

– and soon afterwards there can be multiple tabs with loaded content, in the same session, without using a content process:

Screen recordings of FreeBSD-CURRENT:

• 2019-11-22 07:59 e10s, 2019.10 (20191103135811), FreeBSD-CURRENT.mp4 https://put.re/player/q9jMcFV2.mp4
• 2019-11-22 07:59 e10s, 2019.10 (20191103135811), FreeBSD-CURRENT.zip
• 2019-11-22 08:05 e10s, 2019.10 (20191103135811), FreeBSD-CURRENT.mp4 https://put.re/player/McwzfvR9.mp4
• 2019-11-22 08:05 e10s, 2019.10 (20191103135811), FreeBSD-CURRENT.zip

Screen recording of Linux:

• 2019-11-23 11:37.mp4 https://put.re/player/oySLodsp.mp4
• 2019-11-23 11:37.zip

Impact

I'm not aware of problems arising, from the content process, in FreeBSD-CURRENT or Linux environments. However:

• on FreeBSD-CURRENT, I rarely notice the issue – at the time of writing I can not reproduce it with my very heavily-extended everyday profile
• on Linux, where the issue seems to be consistently reproducible, I have not actively tested with e.g. legacy extensions that are known to fail with Waterfox Classic in multi-process mode.

I don't have easy access to a Mac. If an unexpected content process is a cause of instability in e.g. #1217 (vintage/obsolete environments) then this issue might be treated as a bug.

Meta, tracking: #538

Observation

browser.tabs.remote.force-disable true no longer prevents

☑ Enable multi-process Waterfox

– at about:preferences#general

Distinction

A content process, not a plug-in process.

Here's a separate process for a plug-in with Waterfox Classic in single-process mode (nothing unusual):

[MrAlex94]

Even with e10s disabled, there are various other processes that are spun up :-). It may just be a bit more verbose on Linux in displaying that.