I had the same thing, it failed on FireFox but I did get speedhack to work on Chrome today.
I thought it was just that one game, or maybe a Flash problem.

I did have to "allow" Flash suddenly today to play anything.
And on another game when I go to another tab and come back the game is dead until I reload.
So it does seem like FF is to blame.

------------------------------------------------------------------------------------------------

I've found speed hack rarely ever works anymore. I think it's down to differences in new games, rather than browsers??

Select process plugin-container.exe for firefox in process list after loading the game in firefox flash plugin and then apply speed hack, it should work.  

Yeah when firefox went quantum aka v57+ and copied/borrowed *coughcough*nocopy*coughwheeze*right*coughhaaachoo* they not only curn stomped the add-on extension community but also most of the features that were backwards compatible. So in platimnum quote from angry joe "YOU DONE F****** IT UP" or as i say it *YOU NINETAILED YOU OWN B-GRADE HIND* its better to stick with chrome for the moment or opera.

Atleast in chrome the inbuilt task manager can be used to note down the decimal process number and convert it to hexadecimal and then apply away whatever CE or other 3rd party tools/trainers you want to use on your browser.

I am currently having this issue with both firefox and chrome

Not just speedhacking, but most searches as well (I did get AOB to work on a few games but no speedhack at the same time, and other search did not function)

This is a constant problem and has been going on for a while - I'm not sure what the cause is - tried reinstalling CE and firefox/chrome

I've moved away from Firefox for years now, I've been using Waterfox and I haven't had problems with speedhacking, so in case you're loking for a Firefox-experience but still with legacy feeling (Addons) and full hacking capabilities, I'd suggest it.