CSS in cache gets corrupted - why?

[Dave Royal]

In non-technical forums I often answer Firefox questions or
complaints. Over the past few years one problem has come up again
and again. I reckon I see this every couple of months in one a
sailing forum I frequent. It usually goes something like
this:

"I used to use Firefox but now when I view this forum it's all
screwed up so I changed to Chrome" That is sometimes accompanied
by a description or even a screenshot which shows that the CSS is
missing: white background, blue links, no formatting - you've all
seen it.

This is really easy to fix - clear the cache, control-shift-F5,
etc. But why does it happen? And why has it been happening for
years? I don't see people saying the same about Chrome or IE -
though I'm not so alert to problems in other browsers.

I've googled and not found an answer - though I see it /does/
happen with other browsers and occasionally a reason is found (eg
something installed on Samsungs).

The annoying thing about this problem is that, while for a
technical user it's just an irritation, for a non-technical user
it's often a show-stopper. Unless they're wedded to Firefox they
don't bother to go through any Firefox diagnostic steps, they
just change browser! And there are plenty of equally clueless
posters who will respond with "I use Chrome, never had that
problem!"

I've always put this down to network problems - incomplete
transfers, say. But I don't know if that's plausible (why would
Fx cache an incomplete doc?) and why would it be more prevalent
with Fx - if indeed it is. Today I wondered if it were related to
compressed CSS files, but the sailing forum I mentioned (it's
VB4) doesn't compress them.

Do others come across this. Any theories about the cause?
--
(Remove any numerics from my email address.)

[Ed Mullen]

Never seen this. Of course, it's been many years since I activated a
cache in any browser.

--
Ed Mullen
http://edmullen.net/
Lead me not into temptation (I can find the way myself).

[»Q«]

In <news:mailman.223.142529042...@lists.mozilla.org>,

Dave Royal <da...@dave123royal.com> wrote:

> I reckon I see this every couple of months in one a
> sailing forum I frequent. It usually goes something like
> this:
>
> "I used to use Firefox but now when I view this forum it's all
> screwed up so I changed to Chrome" That is sometimes accompanied
> by a description or even a screenshot which shows that the CSS is
> missing: white background, blue links, no formatting - you've all
> seen it.
>
> This is really easy to fix - clear the cache, control-shift-F5,
> etc. But why does it happen? And why has it been happening for
> years?

I see it sometimes, over the past year or so. I "cure" it with
shift+reload. I don't have a local cache, so I've never thought
it had to do with local caching, at least in my case. The only other
bit of evidence I've got is that it happens for me only on sites
which are slow even when they fully load.

If clearing the cache does get you past it, I guess there might be
clues in the cache itself (before clearing, natch). The only thing I
can think of seems unlikely. If Fx can't get the CSS from the server,
it uses its default CSS. There's no reason to put its own default CSS
into the cache, but maybe it does.

[Dave Royal]

On Mon, 02 Mar 2015 22:51:18 -0600, »Q« wrote:

> I see it sometimes, over the past year or so. I "cure" it with
> shift+reload. I don't have a local cache, so I've never thought it had
> to do with local caching, at least in my case. The only other bit of
> evidence I've got is that it happens for me only on sites which are slow
> even when they fully load.

The only site on which I myself have ever had this problem was one which
often failed to load - it timed out or presented a blank page. It's one
reason why I thought it was a site/network problem. But others seem to
get it on forums which work fine for me. And people often mention it in
passing - so I'm sure that there are many more occurrences than I see.
They're mostly Windows users and probably have AV software which
interferes (I use Linux and Android) so there are lots of possible
causes.

> If clearing the cache does get you past it, I guess there might be clues
> in the cache itself (before clearing, natch). The only thing I can
> think of seems unlikely. If Fx can't get the CSS from the server, it
> uses its default CSS. There's no reason to put its own default CSS into
> the cache, but maybe it does.

IME clearing or overriding the cache /always/ solves it. If I get the
problem again myself I'll look in the cache and then maybe I'll have
evidence for a bug - I'm sure there is one.

[Jeremy Nicoll - ml mozilla groups]

Dave Royal <da...@dave123royal.com> wrote:

>I've always put this down to network problems - incomplete
> transfers, say. But I don't know if that's plausible (why would
> Fx cache an incomplete doc?) and why would it be more prevalent
> with Fx - if indeed it is.

>Do others come across this. Any theories about the cause?

Yes, occasionally. I think it's a problem caused my the proliferation of
websites which use lots of third-party CSS, JS libraries, fonts etc. A
website author has the choice (often) of hosting copies of these extras on
their own server (but obviously that increases bandwidth their users will
use on that server) or just using standard snippets of HTML that usually
pick the things up from CDNs or eg library-specific servers.

I dislike the idea of having 'my' website imbed loads of stuff from
elsewhere, mainly because of the risk that something external changes and my
site no longer works the way I tested it. But lots of people, especially if
the site is generated from templates etc, don't think like that.

There's a FF developer tool - see
https://developer.mozilla.org/en-US/docs/Tools/Web_Console
which enables you to see the successive HTTP requests etc that are caused
when FF tries to load a page - getting the basic HTML then kicking off
subsidiary fetches for everything that's also needed, and so on. It will
show you the times taken for each of these and which bits fail and why that
is, eg timeouts, server errors etc. It might shed some light.


--
Jeremy Nicoll - my opinions are my own.