Caching in %TEMP% folder?

...I've never written anything in NSIS. Can it also do the Javascript escaping trick?
Is that .nsi-file the source code, that needs to be compiled somehow? (if so, how -- or rather, with what?)

Re. 1, 3 and 5: Firefox can be set to clear the cache data itself. Of course, this still leaves a %TEMP%\Cache folder with three or four (NULL-filled) files of about 4K each.
Re. 2: It does seem to speed up Fx if you leave it running an entire day, and visit the same site(s) several times. It definitely does when you disable RAM caching.

But I can't see a way around issue #4, either. I'm prepared to live with that, though...

But anyway, I've written a little PortableFirefox setup file in JScript. It needs to sit in the same folder as PortableFirefox.exe, and only needs to be run once on any PC (though it doesn't hurt).

I'll post it here, in case anyone is interested. It'll need to be adjusted to anyone's preferences; I've added several other absolute paths I found in my prefs.js, some of them customized for my USB key's folder structure.

SetupPFF.js

// Perform the main function of this script
main();
//
function main() {
    var idicPrefs = new ActiveXObject('Scripting.Dictionary');
    idicPrefs.CompareMode = 0; // binary compare
    var lobjFSO = new ActiveXObject('Scripting.FileSystemObject');
    var lobjShell = new ActiveXObject('WScript.Shell');
    //
    // Determine the current script's folder
    var lstrFolder = lobjFSO.GetParentFolderName(WScript.ScriptFullName);
    //
    // Read and backup the existing user.js file
    var lstrUserFileName = lobjFSO.BuildPath(lstrFolder, 'profile\\user.js');
    if(lobjFSO.FileExists(lstrUserFileName) && lobjFSO.GetFile(lstrUserFileName).Size > 0) {
        with(lobjFSO.OpenTextFile(lstrUserFileName)) {
            eval(ReadAll());
            Close();
        }
        with(lobjFSO.GetFile(lstrUserFileName)) {
            var lstrBackupExtension = '-' + createValidFilename(new Date().toLocaleString()) + '.bak';
            try {
                lobjFSO.DeleteFile(Name + lstrBackupExtension);
            }
            catch(lobjError) { };
            Name += lstrBackupExtension;
        }
    }
    //
    //
    // The purpose of this script: set the cache folder to use the local TEMP folder...
    idicPrefs('browser.cache.disk.parent_directory') = lobjShell.ExpandEnvironmentStrings('%TEMP%\\PFF');
    idicPrefs('browser.download.dir') = lobjShell.ExpandEnvironmentStrings('%HOMEDRIVE%%HOMEPATH%\\PFF');
    idicPrefs('conquery.Main.PlugsDir') = lobjFSO.BuildPath(lstrFolder, "profile\\searchplugins");
    idicPrefs('conquery.Main.PlugsDir2') = lobjShell.ExpandEnvironmentStrings('%ProgramFiles%\\Mozilla Firefox\\searchplugins');
    idicPrefs('local_install.base_extension_dir') = lobjFSO.BuildPath(lstrFolder, "XPIs");
    idicPrefs('local_install.default_CSS_editor') = lobjFSO.GetAbsolutePathName(lobjFSO.BuildPath(lstrFolder, "..\\Notepad++\\notepad++.exe"));
    idicPrefs('local_install.default_JS_editor') = lobjFSO.GetAbsolutePathName(lobjFSO.BuildPath(lstrFolder, "..\\Notepad++\\notepad++.exe"));
    idicPrefs('mozex.command.mailer') = lobjFSO.GetAbsolutePathName(lobjFSO.BuildPath(lstrFolder, "..\\PortableThunderbird\\PortableThunderbird.exe"));
    idicPrefs('network.protocol-handler.app.mailto') = lobjFSO.GetAbsolutePathName(lobjFSO.BuildPath(lstrFolder, "..\\PortableThunderbird\\PortableThunderbird.exe"));
    idicPrefs('dafi.viewsource.configPath') = lobjFSO.BuildPath(lstrFolder, "profile\\viewSource.xml");
    //
    //
    // Write out the changed user.js file
    var lstrUserPrefs = '';
    for(var lobjEnum = new Enumerator(idicPrefs); !lobjEnum.atEnd(); lobjEnum.moveNext()) {
        var lstrKey = lobjEnum.item();
        var lvarValue = idicPrefs(lstrKey);
        lstrUserPrefs += 'user_pref("' + lstrKey + '", ';
        switch(typeof(lvarValue)) {
            case 'string' : {
                lstrUserPrefs += '"' + escapeString(lvarValue) + '"';
                break;
            }
            default: {
                lstrUserPrefs += lvarValue;
            }
        }
        lstrUserPrefs += ');\r\n';
    }
    with(lobjFSO.OpenTextFile(lstrUserFileName, 2 /* ForWriting */, true)) {
        Write(lstrUserPrefs);
        Close();
    }
    //
    // Now run Portable Firefox
    if(confirm(lobjShell.ExpandEnvironmentStrings('Portable Firefox setup has successfully been adjusted to computer %COMPUTERNAME%.\n\nDo you want to launch PFF?'))) {
        lobjShell.Run(lobjFSO.BuildPath(lstrFolder, 'PortableFirefox.exe'), 1, false);
    }
    //
    // Clean up
    ldicPrefs = null;
    lobjFSO = null;
    lobjShell = null;
    return;
    //
    // This function will get called by the 'code' in user.js
    function user_pref(astrPref, avarValue) {
        idicPrefs(astrPref) = avarValue;
    }
    //
    // This returns a string fit to be used in JS code.
    function escapeString(astrExpression) {
        var lstrString = '' + astrExpression;
        return lstrString.replace(/\\/g, '\\\\').replace(/\r/g, '\\\r').replace(/\n/g, '\\\n').replace(/\"/g, '\\"');
    }
    //
    // This returns a string valid for use in a filename
    function createValidFilename(astrExpression) {
        var lstrValid = '' + astrExpression;
        lstrValid = lstrValid.replace(/\:/g, ';');
        lstrValid = lstrValid.replace(/\?/g, '¿');
        lstrValid = lstrValid.replace(/[\\\/\:\"\*\?\\|]/g, '_');
        return lstrValid;
    }
}