Game seemed to run fine straight "out of the box", but FOV is terrible.
Tried adding Sui's widescreen FOV fix https://github.com/SuiMachine/W40k-Fire-Warrior---Sui-s-Fix/releases/latest
having seen it on on [url=https://pcgamingwiki.com/wiki/Warhammer_40,000:_Fire_Warrior]https://pcgamingwiki.com/wiki/Warhammer_40,000:_Fire_Warrior[/url]

But it won't run at all now. The config tool that lets you choose controls and resolution will run, but when I try to run the actual game (either by pressing "play singleplayer" from the config tool, or by directly runnning FireWarrior.exe), absolutely nothing happens. It just won't open. Tried deleting the dinput8.dll file that Sui's fix added and now it will run again, but at the terrible default FOV.
Sui says he tested his fix on the GOG 1.5 hotfix version of the game and it worked fine. Has anyone else gotten this fix to work?

I've just done this exact thing. Mine will load with Sui's mod by running the game from FireWarrior.exe in the installation directory

Thanks for confirming. I tried verifying the game and it downloaded 28mb. I tried changing it to display windowed instead of fullscreen and now something happens: A black window appears for a few seconds while the computer processes something, then it closes.

What config/resolution/refresh rate you using?
This is what my config looks like:
<mGfxAdapterIndex>0</mGfxAdapterIndex>
<mGfxWidth>3840</mGfxWidth>
<mGfxHeight>2160</mGfxHeight>
<mGfxRefreshRate>60</mGfxRefreshRate>
<m32Bit>true</m32Bit>
<mWindowed>true</mWindowed>
<mAudioDisableSoftwareFX>true</mAudioDisableSoftwareFX>
<mForceSoftwareAudio>false</mForceSoftwareAudio>

You need the dinput8.dll to load ASI files from Scripts directory. I am kind of surprised that it doesn't start, but figuring it out may be difficult. I have few ideas where the issue may lay.

First off, it'd be good if you tried leaving dinput8.dll in and then removing W40k-fixes.asi from scripts folder to see if it's the ThirteenAG's ASI loader itself or just something in my libraries.

Thanks for the suggestion. It gets a little bit further now with dinput8.dll there, but W40k-fixes.asi removed. Instead of just closing after a few seconds of blackness, it actually shows the paragraph of copyright text for a while, and then it closes.

That is very weird. Without ASI files, but with dinput8.dll still present, the game should run normally (ergo - the ASI loader should check the script folder, load nothing) and just load original Windows libraries and use them. Maybe try running the game's exe as administrator, to make sure it's not just UAC screwing things up... but as I said, I am very confused with this.

May have something to do with GOG Galaxy. Results as I described previously when I launched through GOG Galaxy, but when I launched without it (using either the config tool or the FireWarrior.exe), it did indeed run normally when the ASI file was removed, but still crashed after a few seconds of black screen when the ASI file was put back. An interesting result - GOG Galaxy doesn't seem to like the dinput8.dll even when the ASI file is removed.

So the results are...

dinput8.dll present, W40k-fixes.asi present = A few seconds of black screen then it just closes. (the same whether launched through GOG Galaxy or not)

dinput8.dll present, W40k-fixes.asi absent, launched from GOG Galaxy = shows the paragraph of copyright text for a while, and then it closes.

dinput8.dll present, W40k-fixes.asi absent, launched without GOG Galaxy = runs normally.

dinput8.dll absent, W40k-fixes.asi present = runs normally. (the same whether launched through GOG Galaxy or not)

Sorry to hear that. I completely understand being burntout on a project.

Thanks for the suggestion. The command line parameter definitely works, so it will do.

And thanks for working on the fix in the first place. We're lucky that people like you work to keep old games playable on modern systems, so I appreciate it.