Wide World of Women

I open Firefox this afternoon and I find that my Image Host Grabber is disabled (along with another two addons). I went to their board and found out that if you keep upgrading Firefox they will kill it. There are two alternatives, one is using the about:config page and having a setting to false, or downloading and using the Pale Moon browser which is a "fork" of Firefox. If you are worried that your Firefox settings won't migrate to Pale Moon, there is a tool on the Pale Moon website that you can download. Most Firefox extensions will work with Pale Moon, except Image Toolbar and some others.

http://www.palemoon.org/

No need for palemoon. I tried this and it worked.

What are my options if I want to install unsigned extensions in Firefox?

The Developer Edition and Nightly versions of Firefox will have a setting to disable signature enforcement. There will also be special unbranded versions of Release and Beta that will have this setting, so that add-on developers can work on their add-ons without having to sign every build. To disable signature checks, you will need to set the xpinstall.signatures.required preference to "false".
type about:config into the URL bar in Firefox
in the Search box type xpinstall.signatures.required
double-click the preference, or right-click and selected "Toggle", to set it to false.

Once you set it to false you can use this version that works

http://imagehost-grabber.org/index.php?topic=3457.0

I have heard that fix is only for FF version 43 but won't work in FF 44.

Pale Moon is a fine browser. I've been using it for a couple of years. Waterfox is also good, if you have a 64-Bit system. ( https://www.waterfoxproject.org/ ) ImageHostGrabber works on both.