Installation aborted because the add-on appears to be corrupt.

[gora108]

Hi, the add-on does not work anymore

• textfast could not be verified for use...

[gora108]

Solution
Step-by-Step: Where to Paste the Script

Close SlimBrowser
    Make sure SlimBrowser 18.0.0.0 is fully closed.
Open SlimBrowser and Enable Console
    Start SlimBrowser (from G:\Softwares\SlimBrowser).
    Type about:config in the address bar, press Enter, and click “Accept the Risk.”
    Search for devtools.chrome.enabled.
    If it’s false, double-click to set it to true.
Open the Developer Console
    Press Ctrl+Shift+J—a window pops up.
    You’ll see a blank line or prompt at the bottom (it might say > or just be a cursor). This is where you paste.
Paste the Script
    Copy this exact script:
    javascript

    async function set_addons_as_signed() {
        Components.utils.import("resource://gre/modules/addons/XPIDatabase.jsm");
        Components.utils.import("resource://gre/modules/AddonManager.jsm");
        let addons = await XPIDatabase.getAddonList(a => true);
        for (let addon of addons) {
            if (addon._sourceBundle && !addon._sourceBundle.exists())
                continue;
            if (addon.signedState != AddonManager.SIGNEDSTATE_UNKNOWN)
                continue;
            addon.signedState = AddonManager.SIGNEDSTATE_NOT_REQUIRED;
            AddonManagerPrivate.callAddonListeners("onPropertyChanged",
                                                   addon.wrapper,
                                                   ["signedState"]);
            await XPIDatabase.updateAddonDisabledState(addon);
        }
        XPIDatabase.saveChanges();
    }
    set_addons_as_signed();

In the Developer Console, click the blank line at the bottom.
Right-click > Paste (or press Ctrl+V).
Press Enter to run it.
What to expect: No big output—just a quick flash or “undefined” is normal. It works silently.
Restart and Check
Close SlimBrowser completely.
Reopen it.
Go to about:addons—see if TextFast is enabled.

Where NOT to Paste

Don’t paste in the regular JavaScript console (Ctrl+Shift+K)—that’s for web pages, not browser internals.
Use Ctrl+Shift+J (Developer/Browser Console) instead—it’s for system-level stuff like add-ons.

Next

Tell me:

Did TextFast enable in about:addons?
If not, any error in the console (red text) or same “could not be verified” message?