Does Firefox disable plugins that failed to initialize? - linux

Question

I am trying to test a Mozilla plugin (developed using FireBreath) in the form of an .so shared object file. The plugin was developed on Ubuntu, where it works fine.
I am now trying it under OpenSUSE - so I first symlinked the .so file in ~/.mozilla/plugins:
> ln -s /path/to/npXXX.so ~/.mozilla/plugins/
... and then ran Firefox (7) from command line:
> /path/to/firefox -P myprofile
...
LoadPlugin: failed to initialize shared library libXext.so [libXext.so: cannot open shared object file: No such file or directory]
LoadPlugin: failed to initialize shared library /path/to/npXXX.so [/path/to/npXXX.so: undefined symbol: gtk_widget_get_mapped]
# and the LoadPlugin messages do NOT show a second time - probably because plugin is disabled (via about:addons).
And so I thought to try different stuff to look into this - but first, I restarted Firefox, and realized that on the second run I do not get the "LoadPlugin: failed to initialize" messages anymore! Then I tried removing the plugins symlink, and restarting FF; and adding it again, and restarting FF - still no error messages!
So, this tells me that probably Firefox somehow disabled/blacklisted the plugin (but which one: libXext, npXXX or both?) , but searching (grepping) for (np)XXX in '/path/to/myprofile/blocklist.xml' returns nothing (the plugin should use a email-like id, not those number GUIDs, so I'd expect that string to show in blocklist.xml if it's there).
Does anyone know: is the default behavior of Firefox to disable/blocklist plugins, that fail to load at first? If so, is there a way to force Firefox to load them again (and spit out error messages)? If you'd also have links to where this behavior is documented, it will be much appreciated :)
Many thanks in advance for any answers,
Cheers!
Note: after I stopped seeing the error messages, I did the following:
I am trying "about:plugins": "No enabled plugins found";
then trying "about:addons", and clicking under Plugins: "You don't have any add-ons of this type installed";
This plugin is not embedded in an extension, so nothing new should be added in "about:addons" under "Extensions" - and as expected, nothing new shows there. Under Ubuntu (where all works), just by symlinking the plugin to ~/.mozilla/plugins, the above two locations/screens start showing the plugin info.
This one of the things that puzzle me - if it just showed the plugin as "disabled", maybe I would have had a chance to re-enable it again (to get a new batch of error messages) - however, "about:plugins" and "about:addons" simply show nothing - so there's nothing I can use to enable from there. Which tells me Firefox has used a different method to disable the plugin(s) - but I cannot tell what it is...

Answer 1

Firefox has a cache for XPCOM modules ("fastload cache"), if a module fails to load Firefox won't try again. The cache is reset automatically if an extension is installed or if the application is updated. Starting with Firefox 4 you can also use -purgecaches command line flag to discard the cache.