[Bug 266259] www/firefox 104: high CPU usage

https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=266259

            Bug ID: 266259
           Summary: www/firefox 104: high CPU usage
           Product: Ports & Packages
           Version: Latest
          Hardware: amd64
                OS: Any
            Status: New
          Severity: Affects Some People
          Priority: ---
         Component: Individual Port(s)
          Assignee: ports-bugs@FreeBSD.org
          Reporter: riccardo@torrini.org

After updating www/firefox from 103.0.1 to 104.0_2 (also to 104.0_3 and
104.0.1), I noticed the CPU at 100% with top showing 300+% on the first Firefox
process.

This with 103:
CPU:  0.4% user,  0.0% nice,  1.0% system,  0.1% interrupt, 98.5% idle
Mem: 3077M Active, 5510M Inact, 223M Laundry, 1606M Wired, 1080M Buf, 5328M
Free
Swap: 4273M Total, 4273M Free

  PID USERNAME    THR PRI NICE   SIZE    RES STATE    C   TIME    WCPU COMMAND
 1632 riccardo    170  20    0    14G  2478M select   0  17:49   0.30% firefox
[...and 30 more lines with 0.01% or less...]

This with 104:
2361 riccardo    147  25    0    13G  1279M select   0   6:13 334.54% firefox

Also tried with a clean profile (using refresh from within Firefox, removing
the entire .mozilla/firefox directory and also with a different user).
Returning to 103 stops this problem.

I have many windows open/iconized, with many tabs. And I usually have /home on
NFS. I know it. It's bad behavior, even with lockd and statd. But I also tried
with a local /home on SSD. Same high CPU usage. Forever (at least for a couple
of hours after starting Firefox). No ZFS, only UFS2 both local and remote.

Other tests:
- madpilot@ compiled a 104.0.1 without LTO, same high CPU usage
- madpilot@ saw it on VM under bhyve

Firefox configurations: started 103.0.1/104.0.1 with/without:
- "Use recommended performance settings"
- "Use hardware acceleration when available"
The 103 is still usable, the 104 is not.

Home desktop:
- 13.1-RELEASE-p2 GENERIC amd64
- CPU: Intel(R) Core(TM) i5-7600 CPU @ 3.50GHz (3500.00-MHz K8-class CPU)
- 16GB of RAM
- video: intel: Driver for Intel(R) HD Graphics
- all others pkg updated to latest (all but firefox)

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