Firefox's safe mode - what settings does it reset?

[VanguardLH]

https://support.mozilla.org/t5/Procedures-to-diagnose-and-fix/Troubleshoot-Firefox-issues-using-Safe-Mode/ta-p/1687

says:

Safe Mode temporarily turns off hardware acceleration, resets some
settings, and disables add-ons (extensions and themes) that might be
causing problems.

I can enable/disable hardware acceleration in normal mode.
I only have the default theme (so there is no other choice).
I can disable all extensions in normal mode, too.

But what are the settings that are reset (their defaults used) within a
safe mode session of Firefox? I can go into about:config and sort by
Status to get the "user set" settings at the top of the listing.
However, the majority of them are due to USING Firefox, not user tweaks.
There are over 500 settings in "user set" status. Many are changed by
Firefox. Many are changed by add-ons (which would be ineffective when
testing with all add-ons disabled).

I'm having a problem with Firefox being really, really, really slow when
it loads a new document (web page). Once the page renders, it's quick,
like for image load, videos, etc. It's getting the document to load.
It's not a problem with a slow connection. Speedtest.net shows I have
233 Mbps for downstream speed (and my ISP's bandwidth test page shows
the same). I've tried disabling the anti-virus software, and also tried
disabling its HTTPS scanning feature (using a root cert in Firefox's
private cert store and performing a MITM scheme to interrogate HTTPS web
traffic for nasties).

I was going to try using Refresh that creates an new and empty Firefox
profile but then I decided to try Firefox's safe mode. It got snappy
again. Well, I can disable hardware acceleration, add-ons, and there is
no theme to select and load Firefox in its normal mode but the slow
document load is still exhibited. So it is something more in Firefox
than just those changes for its safe mode. Alas, I cannot find just
what settings are changed (to use their defaults) during a safe mode
session in Firefox to see which of those might be causing the slow down
in normal mode.

Lots of users have been complaining about severe slowness in Firefox
since the version 52 release. For me, using safe mode makes Firefox
snappy again but obviously I lose the ability to use add-ons. I can
make all the changes to Firefox in normal mode that are performed by its
safe mode except whatever are those secretive settings. I'm trying to
narrow down why Firefox 52 became so much slower. I have other users
complaining about how FF 52 got slow. I see lots of posts by other
users having the same problem. I really don't want to go back to
version 51 and then keep experimenting on a test host for when the
slowness gets addressed in a future version of Firefox.

If I knew what were the settings changed in safe mode (presumably to
their defaults) then I can test each one to see when the slowness
reappears when it is not at its default value. I do the other safe mode
changes while loading FF in its normal mode. I've done those. No help.
So the last part of safe mode in Firefox are those changed settings.

Maybe a Refresh in Firefox would eliminate the slowness but then I've
not discovered the cause. That would start with a new profile with no
add-ons (not a problem since I've test with all disabled) and with
default settings - but I wouldn't know which setting(s) effected the
slowness. So the problem would likely resurface as I tweaked my Firefox
profile like I had it before.

http://kb.mozillazine.org/Safe_mode

That doesn't mention any settings changed in safe mode. I don't have
any customized user*.css files (I don't have any of those in my Firefox
profile). It says:

Safe Mode temporarily affects the following:
All extensions are disabled. (1)
The default theme is used, without a persona. (2)
The Just-in-time (JIT) JavaScript compiler is disabled.
The userChrome.css and userContent.css files are ignored. (3)
The default toolbar layout is used.
Hardware acceleration is disabled. (1)

(1) Tried these in normal mode. No effect. Firefox still slow on
initial document load.
(2) There is only one theme: the default one.
(3) Don't have these files.

Before trying a new profile (doing a Refresh), I'd still like to test
the features of safe mode but while in normal mode to isolate what it is
in safe mode that eliminates the slowness in FF 52. Until I do a
Refresh, I don't know that a new profile will help. I don't want to
create a new profile, hail the return of a snappy FF, and then end up
with it getting slow again as I reapply my tweaks to its settings.

[Richmond]

>
> But what are the settings that are reset (their defaults used) within a
> safe mode session of Firefox? I can go into about:config and sort by
> Status to get the "user set" settings at the top of the listing.
> However, the majority of them are due to USING Firefox, not user tweaks.
> There are over 500 settings in "user set" status. Many are changed by
> Firefox. Many are changed by add-ons (which would be ineffective when
> testing with all add-ons disabled).
>

If you use about:support and scroll down there is a list of "important
modified preferences". I am not sure if it's all the important ones, or
if they are all important, but it is a shorter list then the one you got
by sorting on status.

[EE]

According to Mozillazine Knowledge Base:

Safe Mode has no effect on the following:
The status of plugins is not affected.
Custom preferences are not affected.

The preferences that you set are not affected, so presumably your
preference settings are not the cause of the problem.

[Millwood]

IMHO the "right way" to separate you settings from a fundamental bug is
to create an new profile and test under it. That gets you back to the
install defaults.

[J. P. Gilliver (John)]

In message
<mailman.1760.149248110...@lists.mozilla.org>,
VanguardLH <V...@nguard.LH> writes:
[]

>http://kb.mozillazine.org/Safe_mode
>
>That doesn't mention any settings changed in safe mode. I don't have
>any customized user*.css files (I don't have any of those in my Firefox
>profile). It says:
>
> Safe Mode temporarily affects the following:
> All extensions are disabled. (1)
> The default theme is used, without a persona. (2)
> The Just-in-time (JIT) JavaScript compiler is disabled.
> The userChrome.css and userContent.css files are ignored. (3)
> The default toolbar layout is used.
> Hardware acceleration is disabled. (1)

[]
I don't know if the 'script compiler will have any effect on this, but:

I find some pages take ages to load because they're waiting for
something from some site I have blocked in my hosts file. Do you have
such? If so, does safe mode make any difference to what happens?

I don't know _what_ the pages are waiting for from the blocked sites,
nor why they take so long to realise nothing is coming. I can only
_assume_ they have loaded scripts from sites I haven't blocked (or
contain the scripts natively), and those scripts try to access the
blocked sites and have a longish timeout. But I might be quite wrong
about that.

(I know Firefox is waiting for something from those sites, because it
waits long enough that I can see "waiting for" or similar in the status
line. [Status4evar])
--
J. P. Gilliver. UMRA: 1960/<1985 MB++G()AL-IS-Ch++(p)Ar@T+H+Sh0!:`)DNAf

A closed mouth gathers no foot.

[VanguardLH]

"J. P. Gilliver (John)" <G6JP...@255soft.uk> wrote:

> I don't know if the 'script compiler will have any effect on this, but:
>
> I find some pages take ages to load because they're waiting for
> something from some site I have blocked in my hosts file. Do you have
> such? If so, does safe mode make any difference to what happens?

Nothing in the 'hosts' file (other than the 127.0.0.1 localhost). I've
never bothered with pre-compiled 'hosts' file (e.g., MVPS Hosts). They
are huge and incur a delay because the text file gets opened on every
DNS request and sequentially searched for a matching entry. They cannot
block on a domain, only a host name (hence the name of the file). You
had to use HostsMan to keep the pre-compiled 'hosts' file up to date.

> (I know Firefox is waiting for something from those sites, because it
> waits long enough that I can see "waiting for" or similar in the status
> line. [Status4evar])

See my reply to Millwood. Further research found users reporting DNS
caching in FF 52 is slower. Firefox has its own internal DNS cache; see
http://ccm.net/faq/555-disabling-the-dns-cache-in-mozilla-firefox.
That's how it can prefetch DNS lookup for objects in a web page and even
for the web page you visit into its own DNS cache.

I've had DNS prefetching (network.dns.disablePrefetch = True) in Firefox
disabled for as long as I can remember using Firefox. I've also had
linked object prefetch (network.prefetch-next) disabled for a long time
which has Firefox downloading pages linked in the visited page that I
may never visit (i.e., wasted bandwidth, privacy issues). By reverting
those back to their defaults, the sluggishness in Firefox became masked.
I say masked because the problem is still there unless those features
are employed to speed it up. Something got slower in FF52 without those
features since I didn't notice the slowdown in prior versions with those
features disabled.